{"id":"3660b216-a296-4b84-8478-1f899f06ea5d","name":"Reverse Linked List (pointer Iterative)","description":"1. You are given a partially written LinkedList class.\r\n2. Here is a list of existing functions:\r\n 2.1 addLast - adds a new element with given value to the end of Linked List\r\n 2.2. display - Prints the elements of linked list from front to end in a single line. \r\n All elements are separated by space\r\n 2.3. size - Returns the number of elements in the linked list.\r\n 2.4. removeFirst - Removes the first element from Linked List. \r\n 2.5. getFirst - Returns the data of first element. \r\n 2.6. getLast - Returns the data of last element. \r\n 2.7. getAt - Returns the data of element available at the index passed. \r\n 2.8. addFirst - adds a new element with given value in front of linked list.\r\n 2.9. addAt - adds a new element at a given index.\r\n 2.10. removeLast - removes the last element of linked list.\r\n 2.11. removeAt - remove an element at a given index\r\n3. You are required to complete the body of reversePI function. The function should be an iterative function and should reverse the contents of linked list by changing the \"next\" property of nodes.\r\n4. Input and Output is managed for you.","inputFormat":"Input is managed for you","outputFormat":"Output is managed for you","constraints":"None","sampleCode":{"cpp":{"code":"#include <iostream>\nusing namespace std;\nclass node{\n public:\n int val;\n node* next;\n \n\n};\nclass LinkedList {\n public: node* head=nullptr;\n node* tail=nullptr;\n int size_=0;\n\nvoid insert_at_tail(int val){\n if(head==NULL){\n node *newnode = new node;\n newnode->val=val;\n newnode->next=NULL;\n head=newnode;\n\n }\n else{\n node *newnode = new node;\n newnode->val=val;\n newnode->next=NULL;\n node *temp = head;\n while(temp->next!=NULL){\n temp=temp->next;\n }\n temp->next = newnode;\n }\n\n}\nvoid insertion_at_head(int val){\n node *newnode = new node;\n newnode->val=val;\n newnode->next=NULL;\n if(head==NULL){\n head=newnode;\n }\n else{\n newnode ->next =head;\n head = newnode;\n }\n\n}\nvoid print (){\n node *temp =head;\n if(head==NULL){\n cout << \"0\" << endl;\n return;\n }\n while(temp!=NULL){\n cout<<temp->val<<\" \";\n temp=temp->next;\n }\n cout << endl;\n}\nvoid deletion_at_head(){\n if(head==NULL) return;\n node *temp=head;\n head=head->next;\n delete temp;\n\n}\nvoid deletion_at_tail(){\n if(head==NULL) return;\n node* previous=NULL;\n node* temp=head;\n while(temp->next!=NULL){\n previous=temp;\n temp=temp->next;\n }\n previous->next = NULL;\n delete temp; \n}\n\n\nvoid last(){\n node* temp=head;\n while(temp->next!=NULL){\n temp=temp->next;\n }\n cout << temp->val << endl;\n}\nint size(){\n int cnt=0;\n node* temp=head;\n while(temp!=NULL){\n temp=temp->next;\n cnt++;\n }\n return cnt;\n}\nvoid first(){\n cout << head->val << endl;\n}\n\nnode* getAt(int p){\n int cnt=0;\n node* temp=head;\n while(cnt < p){\n cnt++;\n temp=temp->next;\n }\n cout << temp->val << endl;\n return temp;\n}\n\nvoid addAt(int pos,int data){\n if(pos==0){\n insertion_at_head(data);\n return;\n }\n node* newnode=new node;\n newnode->val=data;\n int cnt=0;\n node* temp=head;\n while(cnt<pos-1){\n cnt++;\n temp=temp->next;\n }\n newnode->next=temp->next;\n temp->next=newnode;\n \n \n}\n\nvoid removeAt(int pos){ \n if(pos==0){\n deletion_at_head();\n return;\n }\n int cnt=0;\n node* temp=head;\n while(cnt<pos-1){\n cnt++;\n temp=temp->next;\n }\n temp->next = temp->next->next;\n}\n\nvoid reverse_di(){\n int left = 0;\n int right = size() - 1;\n while(left < right){\n node* templ = getAt( left);\n node* tempr = getAt( right);\n \n int temp = templ->val;\n templ->val = tempr->val;\n tempr->val = temp;\n left++;\n right--;\n }\n}\nvoid reverse_pi(){\n // write your code here\n}\n};\nint main() {\n LinkedList l1;\n string s;\n cin >> s;\n while(s!=\"quit\"){\n if(s==\"addLast\"){\n int data;\n cin>> data;\n l1.insert_at_tail(data);\n }\n else if(s==\"addFirst\"){\n int data;\n cin>> data;\n l1.insertion_at_head(data);\n }\n else if(s==\"getFirst\"){\n if(l1.head!=NULL){\n l1.first();\n }else{\n cout << \"List is empty\" << endl;\n }\n }\n else if(s==\"getLast\"){\n if(l1.head!=NULL){\n l1.last();\n } \n else\n {\n cout<<\"List is empty\";\n }\n \n }\n else if(s==\"removeFirst\"){\n if(l1.head!=NULL){\n l1.deletion_at_head();\n }\n else{\n cout << \"List is empty\" << endl; \n }\n }\n \n else if(s==\"getAt\"){\n if(l1.head!=NULL){\n int i;\n cin >> i; \n if(i>=l1.size()){\n cout << \"Invalid arguments\" << endl;\n }\n else{\n l1.getAt(i);\n }\n }\n else\n {\n cout<<\"List is empty\";\n }\n \n }\n else if(s==\"display\"){\n if(l1.head!=NULL){\n l1.print();\n }\n else{\n cout << endl;\n }\n }\n else if(s==\"size\"){\n if(l1.head!=NULL){\n cout << l1.size() << endl;\n }\n }\n else if(s==\"addAt\"){\n int val,i;\n cin >> i >> val;\n if(i>l1.size()){\n cout << \"Invalid arguments\" << endl;\n }\n else{\n l1.addAt(i,val);\n }\n }\n else if(s == \"removeLast\"){\n if(l1.head!=NULL){\n l1.deletion_at_tail();\n }\n else{\n cout << \"List is empty\" << endl; \n }\n }\n else if(s == \"removeAt\"){\n if(l1.head!=NULL){\n int i;\n cin >> i; \n if(i>l1.size()){\n cout << \"Invalid arguments\" << endl;\n }\n else{\n l1.removeAt(i);\n }\n }\n else{\n cout << \"List is empty\" << endl; \n }\n }else if(s == \"reverseDI\"){\n if(l1.head!=NULL){\n l1.reverse_di();\n }\n else{\n cout << \"List is empty\" << endl; \n }\n }\n else if(s == \"reversePI\"){\n if(l1.head!=NULL){\n l1.reverse_pi();\n }\n else{\n cout << \"List is empty\" << endl; \n }\n \n }\n cin >> s;\n }\n \n}"},"java":{"code":"import java.io.*;\r\nimport java.util.*;\r\n\r\npublic class Main {\r\n public static class Node {\r\n int data;\r\n Node next;\r\n }\r\n\r\n public static class LinkedList {\r\n Node head;\r\n Node tail;\r\n int size;\r\n\r\n void addLast(int val) {\r\n Node temp = new Node();\r\n temp.data = val;\r\n temp.next = null;\r\n\r\n if (size == 0) {\r\n head = tail = temp;\r\n } else {\r\n tail.next = temp;\r\n tail = temp;\r\n }\r\n\r\n size++;\r\n }\r\n\r\n public int size() {\r\n return size;\r\n }\r\n\r\n public void display() {\r\n for (Node temp = head; temp != null; temp = temp.next) {\r\n System.out.print(temp.data + \" \");\r\n }\r\n System.out.println();\r\n }\r\n\r\n public void removeFirst() {\r\n if (size == 0) {\r\n System.out.println(\"List is empty\");\r\n } else if (size == 1) {\r\n head = tail = null;\r\n size = 0;\r\n } else {\r\n head = head.next;\r\n size--;\r\n }\r\n }\r\n\r\n public int getFirst() {\r\n if (size == 0) {\r\n System.out.println(\"List is empty\");\r\n return -1;\r\n } else {\r\n return head.data;\r\n }\r\n }\r\n\r\n public int getLast() {\r\n if (size == 0) {\r\n System.out.println(\"List is empty\");\r\n return -1;\r\n } else {\r\n return tail.data;\r\n }\r\n }\r\n\r\n public int getAt(int idx) {\r\n if (size == 0) {\r\n System.out.println(\"List is empty\");\r\n return -1;\r\n } else if (idx < 0 || idx >= size) {\r\n System.out.println(\"Invalid arguments\");\r\n return -1;\r\n } else {\r\n Node temp = head;\r\n for (int i = 0; i < idx; i++) {\r\n temp = temp.next;\r\n }\r\n return temp.data;\r\n }\r\n }\r\n\r\n public void addFirst(int val) {\r\n Node temp = new Node();\r\n temp.data = val;\r\n temp.next = head;\r\n head = temp;\r\n\r\n if (size == 0) {\r\n tail = temp;\r\n }\r\n\r\n size++;\r\n }\r\n\r\n public void addAt(int idx, int val) {\r\n if (idx < 0 || idx > size) {\r\n System.out.println(\"Invalid arguments\");\r\n } else if (idx == 0) {\r\n addFirst(val);\r\n } else if (idx == size) {\r\n addLast(val);\r\n } else {\r\n Node node = new Node();\r\n node.data = val;\r\n\r\n Node temp = head;\r\n for (int i = 0; i < idx - 1; i++) {\r\n temp = temp.next;\r\n }\r\n node.next = temp.next;\r\n\r\n temp.next = node;\r\n size++;\r\n }\r\n }\r\n\r\n public void removeLast() {\r\n if (size == 0) {\r\n System.out.println(\"List is empty\");\r\n } else if (size == 1) {\r\n head = tail = null;\r\n size = 0;\r\n } else {\r\n Node temp = head;\r\n for (int i = 0; i < size - 2; i++) {\r\n temp = temp.next;\r\n }\r\n\r\n tail = temp;\r\n tail.next = null;\r\n size--;\r\n }\r\n }\r\n\r\n public void removeAt(int idx) {\r\n if (idx < 0 || idx >= size) {\r\n System.out.println(\"Invalid arguments\");\r\n } else if (idx == 0) {\r\n removeFirst();\r\n } else if (idx == size - 1) {\r\n removeLast();\r\n } else {\r\n Node temp = head;\r\n for (int i = 0; i < idx - 1; i++) {\r\n temp = temp.next;\r\n }\r\n\r\n temp.next = temp.next.next;\r\n size--;\r\n }\r\n }\r\n\r\n private Node getNodeAt(int idx) {\r\n Node temp = head;\r\n for (int i = 0; i < idx; i++) {\r\n temp = temp.next;\r\n }\r\n return temp;\r\n }\r\n\r\n public void reverseDI() {\r\n int li = 0;\r\n int ri = size - 1;\r\n while(li < ri){\r\n Node left = getNodeAt(li);\r\n Node right = getNodeAt(ri);\r\n\r\n int temp = left.data;\r\n left.data = right.data;\r\n right.data = temp;\r\n\r\n li++;\r\n ri--;\r\n }\r\n }\r\n \r\n public void reversePI(){\r\n // write your code here\r\n }\r\n }\r\n\r\n public static void main(String[] args) throws Exception {\r\n BufferedReader br = new BufferedReader(new InputStreamReader(System.in));\r\n LinkedList list = new LinkedList();\r\n\r\n String str = br.readLine();\r\n while (str.equals(\"quit\") == false) {\r\n if (str.startsWith(\"addLast\")) {\r\n int val = Integer.parseInt(str.split(\" \")[1]);\r\n list.addLast(val);\r\n } else if (str.startsWith(\"size\")) {\r\n System.out.println(list.size());\r\n } else if (str.startsWith(\"display\")) {\r\n list.display();\r\n } else if (str.startsWith(\"removeFirst\")) {\r\n list.removeFirst();\r\n } else if (str.startsWith(\"getFirst\")) {\r\n int val = list.getFirst();\r\n if (val != -1) {\r\n System.out.println(val);\r\n }\r\n } else if (str.startsWith(\"getLast\")) {\r\n int val = list.getLast();\r\n if (val != -1) {\r\n System.out.println(val);\r\n }\r\n } else if (str.startsWith(\"getAt\")) {\r\n int idx = Integer.parseInt(str.split(\" \")[1]);\r\n int val = list.getAt(idx);\r\n if (val != -1) {\r\n System.out.println(val);\r\n }\r\n } else if (str.startsWith(\"addFirst\")) {\r\n int val = Integer.parseInt(str.split(\" \")[1]);\r\n list.addFirst(val);\r\n } else if (str.startsWith(\"addAt\")) {\r\n int idx = Integer.parseInt(str.split(\" \")[1]);\r\n int val = Integer.parseInt(str.split(\" \")[2]);\r\n list.addAt(idx, val);\r\n } else if (str.startsWith(\"removeLast\")) {\r\n list.removeLast();\r\n } else if (str.startsWith(\"removeAt\")) {\r\n int idx = Integer.parseInt(str.split(\" \")[1]);\r\n list.removeAt(idx);\r\n } else if(str.startsWith(\"reverseDI\")){\r\n list.reverseDI();\r\n } else if(str.startsWith(\"reversePI\")){\r\n list.reversePI();\r\n }\r\n str = br.readLine();\r\n }\r\n }\r\n}"},"python":{"code":"class Node:\n\n def __init__(self):\n self.data = 0\n self.next = None\n\n\nclass LinkedList:\n\n def __init__(self):\n self.head = None\n self.tail = None\n self.size = 0\n\n def addLast(self, val):\n temp = Node()\n temp.data = val\n temp.next = None\n\n if self.size == 0:\n self.head = self.tail = temp\n else:\n self.tail.next = temp\n self.tail = temp\n self.size += 1\n \n def getNodeAt(self, idx):\n temp = self.head\n i = 0\n while i < idx:\n temp = temp.next\n i += 1\n return temp\n \n def display(self):\n temp = self.head\n while temp is not None:\n print(temp.data, end = \" \")\n temp = temp.next\n print()\n \n def removeFirst(self):\n if self.size == 0:\n print(\"List is empty\")\n elif self.size == 1:\n self.head = self.tail = None\n self.size = 0\n else:\n self.head = self.head.next\n self.size -= 1\n \n def getFirst(self):\n if self.size == 0:\n print(\"List is empty\")\n return -1\n else:\n return self.head.data\n\n def getLast(self):\n if self.size == 0:\n print(\"List is empty\")\n return -1\n else:\n return self.tail.data\n \n def getAt(self, idx):\n if self.size == 0:\n print(\"List is empty\")\n return -1\n elif idx < 0 or idx >= self.size:\n print(\"Invalid arguments\")\n return -1\n else:\n temp = self.head\n i = 0\n while i < idx:\n temp = temp.next\n i += 1\n return temp.data\n \n def addFirst(self, val):\n temp = Node()\n temp.data = val\n temp.next = self.head\n self.head = temp\n\n if self.size == 0:\n self.tail = temp\n\n self.size += 1\n \n def removeAt(self, idx):\n if idx < 0 or idx >= self.size:\n print(\"Invalid arguments\")\n elif idx == 0:\n self.removeFirst()\n elif idx == self.size - 1:\n self.removeLast()\n else:\n temp = self.head\n i = 0\n while i < idx - 1:\n temp = temp.next\n i += 1\n\n temp.next = temp.next.next\n self.size -= 1\n\n def addAt(self, idx, val):\n if idx < 0 or idx > self.size:\n print(\"Invalid arguments\")\n elif idx == 0:\n self.addFirst(val)\n elif idx == self.size:\n self.addLast(val)\n else:\n node = Node()\n node.data = val\n\n temp = self.head\n i = 0\n while i < idx - 1:\n temp = temp.next\n i += 1\n node.next = temp.next\n\n temp.next = node\n self.size += 1\n \n def removeLast(self):\n if self.size == 0:\n print(\"List is empty\")\n elif self.size == 1:\n self.head = self.tail = None\n self.size = 0\n else:\n temp = self.head\n i = 0\n while i < self.size - 2:\n temp = temp.next\n i += 1\n\n self.tail = temp\n self.tail.next = None\n self.size -= 1\n \n def reverseDI(self):\n left=0\n right=self.size-1\n while(left<right):\n temp1 = self.getNodeAt(left)\n temp2 = self.getNodeAt(right)\n temp = temp1.data\n temp1.data = temp2.data\n temp2.data = temp\n left+=1\n right-=1\n \n \nl1 = LinkedList()\nwhile True:\n cmd=input().split(\" \")\n if \"addLast\" in cmd[0]:\n val=int(cmd[1])\n l1.addLast(val)\n \n elif \"getFirst\" in cmd[0]:\n ans=l1.getFirst()\n if(ans!=-1):\n print(ans)\n \n elif \"getLast\" in cmd[0]:\n ans=l1.getLast()\n if(ans!=-1):\n print(ans)\n \n elif \"getAt\" in cmd[0]:\n idx=int(cmd[1])\n ans=l1.getAt(idx)\n if(ans!=-1):\n print(ans)\n \n elif \"removeFirst\" in cmd[0]:\n l1.removeFirst()\n \n elif \"removeLast\" in cmd[0]:\n l1.removeLast()\n \n elif \"addFirst\" in cmd[0]:\n val=int(cmd[1])\n l1.addFirst(val)\n \n elif \"quit\" in cmd[0]:\n break\n \n elif \"display\" in cmd[0]:\n l1.display()\n \n elif \"size\" in cmd[0]:\n print(l1.size)\n \n elif \"addAt\" in cmd[0]:\n idx=int(cmd[1])\n val=int(cmd[2])\n l1.addAt(idx,val)\n \n elif \"removeAt\" in cmd[0]:\n idx=int(cmd[1])\n l1.removeAt(idx)\n \n elif \"reverseDI\" in cmd[0]:\n l1.reverseDI()"}},"points":10,"difficulty":"easy","sampleInput":"addFirst 10\r\naddFirst 20\r\naddLast 30\r\naddLast 40\r\naddLast 50\r\naddFirst 60\r\nremoveAt 2\r\ndisplay\r\nreversePI\r\ndisplay\r\nquit","sampleOutput":"60 20 30 40 50 \r\n50 40 30 20 60 \r\n","questionVideo":"https://www.youtube.com/embed/iAEvqhaeD88","hints":[],"associated":[],"solutionSeen":false,"tags":[],"meta":{"path":[{"id":0,"name":"home"},{"id":"0c54b191-7b99-4f2c-acb3-e7f2ec748b2a","name":"Data Structures and Algorithms","slug":"data-structures-and-algorithms","type":0},{"id":"91027ef1-2784-45bf-8143-cc6af4560105","name":"Linked Lists For Beginners","slug":"linked-lists-for-beginners","type":0},{"id":"43b3c352-ebd9-4520-a2f8-991fd5a7d142","name":"Reverse Linked List (pointer Iterative)","slug":"reverse-linked-list-pointer-iterative","type":1}],"next":{"id":"eaf6c6b6-5167-4d95-b183-08c2c5deb5bd","name":"Reverse Linked List (pointer Iterative)","type":3,"slug":"reverse-linked-list-pointer-iterative"},"prev":{"id":"610b62ff-d616-4f1e-a82a-5a3afb81cd74","name":"Reverse A Linked List (data Iterative)","type":3,"slug":"reverse-a-linked-list-data-iterative"}}}

Reverse Linked List (pointer Iterative)

1. You are given a partially written LinkedList class. 2. Here is a list of existing functions: 2.1 addLast - adds a new element with given value to the end of Linked List 2.2. display - Prints the elements of linked list from front to end in a single line. All elements are separated by space 2.3. size - Returns the number of elements in the linked list. 2.4. removeFirst - Removes the first element from Linked List. 2.5. getFirst - Returns the data of first element. 2.6. getLast - Returns the data of last element. 2.7. getAt - Returns the data of element available at the index passed. 2.8. addFirst - adds a new element with given value in front of linked list. 2.9. addAt - adds a new element at a given index. 2.10. removeLast - removes the last element of linked list. 2.11. removeAt - remove an element at a given index 3. You are required to complete the body of reversePI function. The function should be an iterative function and should reverse the contents of linked list by changing the "next" property of nodes. 4. Input and Output is managed for you.

{"id":"3660b216-a296-4b84-8478-1f899f06ea5d","name":"Reverse Linked List (pointer Iterative)","description":"1. You are given a partially written LinkedList class.\r\n2. Here is a list of existing functions:\r\n 2.1 addLast - adds a new element with given value to the end of Linked List\r\n 2.2. display - Prints the elements of linked list from front to end in a single line. \r\n All elements are separated by space\r\n 2.3. size - Returns the number of elements in the linked list.\r\n 2.4. removeFirst - Removes the first element from Linked List. \r\n 2.5. getFirst - Returns the data of first element. \r\n 2.6. getLast - Returns the data of last element. \r\n 2.7. getAt - Returns the data of element available at the index passed. \r\n 2.8. addFirst - adds a new element with given value in front of linked list.\r\n 2.9. addAt - adds a new element at a given index.\r\n 2.10. removeLast - removes the last element of linked list.\r\n 2.11. removeAt - remove an element at a given index\r\n3. You are required to complete the body of reversePI function. The function should be an iterative function and should reverse the contents of linked list by changing the \"next\" property of nodes.\r\n4. Input and Output is managed for you.","inputFormat":"Input is managed for you","outputFormat":"Output is managed for you","constraints":"None","sampleCode":{"cpp":{"code":"#include <iostream>\nusing namespace std;\nclass node{\n public:\n int val;\n node* next;\n \n\n};\nclass LinkedList {\n public: node* head=nullptr;\n node* tail=nullptr;\n int size_=0;\n\nvoid insert_at_tail(int val){\n if(head==NULL){\n node *newnode = new node;\n newnode->val=val;\n newnode->next=NULL;\n head=newnode;\n\n }\n else{\n node *newnode = new node;\n newnode->val=val;\n newnode->next=NULL;\n node *temp = head;\n while(temp->next!=NULL){\n temp=temp->next;\n }\n temp->next = newnode;\n }\n\n}\nvoid insertion_at_head(int val){\n node *newnode = new node;\n newnode->val=val;\n newnode->next=NULL;\n if(head==NULL){\n head=newnode;\n }\n else{\n newnode ->next =head;\n head = newnode;\n }\n\n}\nvoid print (){\n node *temp =head;\n if(head==NULL){\n cout << \"0\" << endl;\n return;\n }\n while(temp!=NULL){\n cout<<temp->val<<\" \";\n temp=temp->next;\n }\n cout << endl;\n}\nvoid deletion_at_head(){\n if(head==NULL) return;\n node *temp=head;\n head=head->next;\n delete temp;\n\n}\nvoid deletion_at_tail(){\n if(head==NULL) return;\n node* previous=NULL;\n node* temp=head;\n while(temp->next!=NULL){\n previous=temp;\n temp=temp->next;\n }\n previous->next = NULL;\n delete temp; \n}\n\n\nvoid last(){\n node* temp=head;\n while(temp->next!=NULL){\n temp=temp->next;\n }\n cout << temp->val << endl;\n}\nint size(){\n int cnt=0;\n node* temp=head;\n while(temp!=NULL){\n temp=temp->next;\n cnt++;\n }\n return cnt;\n}\nvoid first(){\n cout << head->val << endl;\n}\n\nnode* getAt(int p){\n int cnt=0;\n node* temp=head;\n while(cnt < p){\n cnt++;\n temp=temp->next;\n }\n cout << temp->val << endl;\n return temp;\n}\n\nvoid addAt(int pos,int data){\n if(pos==0){\n insertion_at_head(data);\n return;\n }\n node* newnode=new node;\n newnode->val=data;\n int cnt=0;\n node* temp=head;\n while(cnt<pos-1){\n cnt++;\n temp=temp->next;\n }\n newnode->next=temp->next;\n temp->next=newnode;\n \n \n}\n\nvoid removeAt(int pos){ \n if(pos==0){\n deletion_at_head();\n return;\n }\n int cnt=0;\n node* temp=head;\n while(cnt<pos-1){\n cnt++;\n temp=temp->next;\n }\n temp->next = temp->next->next;\n}\n\nvoid reverse_di(){\n int left = 0;\n int right = size() - 1;\n while(left < right){\n node* templ = getAt( left);\n node* tempr = getAt( right);\n \n int temp = templ->val;\n templ->val = tempr->val;\n tempr->val = temp;\n left++;\n right--;\n }\n}\nvoid reverse_pi(){\n // write your code here\n}\n};\nint main() {\n LinkedList l1;\n string s;\n cin >> s;\n while(s!=\"quit\"){\n if(s==\"addLast\"){\n int data;\n cin>> data;\n l1.insert_at_tail(data);\n }\n else if(s==\"addFirst\"){\n int data;\n cin>> data;\n l1.insertion_at_head(data);\n }\n else if(s==\"getFirst\"){\n if(l1.head!=NULL){\n l1.first();\n }else{\n cout << \"List is empty\" << endl;\n }\n }\n else if(s==\"getLast\"){\n if(l1.head!=NULL){\n l1.last();\n } \n else\n {\n cout<<\"List is empty\";\n }\n \n }\n else if(s==\"removeFirst\"){\n if(l1.head!=NULL){\n l1.deletion_at_head();\n }\n else{\n cout << \"List is empty\" << endl; \n }\n }\n \n else if(s==\"getAt\"){\n if(l1.head!=NULL){\n int i;\n cin >> i; \n if(i>=l1.size()){\n cout << \"Invalid arguments\" << endl;\n }\n else{\n l1.getAt(i);\n }\n }\n else\n {\n cout<<\"List is empty\";\n }\n \n }\n else if(s==\"display\"){\n if(l1.head!=NULL){\n l1.print();\n }\n else{\n cout << endl;\n }\n }\n else if(s==\"size\"){\n if(l1.head!=NULL){\n cout << l1.size() << endl;\n }\n }\n else if(s==\"addAt\"){\n int val,i;\n cin >> i >> val;\n if(i>l1.size()){\n cout << \"Invalid arguments\" << endl;\n }\n else{\n l1.addAt(i,val);\n }\n }\n else if(s == \"removeLast\"){\n if(l1.head!=NULL){\n l1.deletion_at_tail();\n }\n else{\n cout << \"List is empty\" << endl; \n }\n }\n else if(s == \"removeAt\"){\n if(l1.head!=NULL){\n int i;\n cin >> i; \n if(i>l1.size()){\n cout << \"Invalid arguments\" << endl;\n }\n else{\n l1.removeAt(i);\n }\n }\n else{\n cout << \"List is empty\" << endl; \n }\n }else if(s == \"reverseDI\"){\n if(l1.head!=NULL){\n l1.reverse_di();\n }\n else{\n cout << \"List is empty\" << endl; \n }\n }\n else if(s == \"reversePI\"){\n if(l1.head!=NULL){\n l1.reverse_pi();\n }\n else{\n cout << \"List is empty\" << endl; \n }\n \n }\n cin >> s;\n }\n \n}"},"java":{"code":"import java.io.*;\r\nimport java.util.*;\r\n\r\npublic class Main {\r\n public static class Node {\r\n int data;\r\n Node next;\r\n }\r\n\r\n public static class LinkedList {\r\n Node head;\r\n Node tail;\r\n int size;\r\n\r\n void addLast(int val) {\r\n Node temp = new Node();\r\n temp.data = val;\r\n temp.next = null;\r\n\r\n if (size == 0) {\r\n head = tail = temp;\r\n } else {\r\n tail.next = temp;\r\n tail = temp;\r\n }\r\n\r\n size++;\r\n }\r\n\r\n public int size() {\r\n return size;\r\n }\r\n\r\n public void display() {\r\n for (Node temp = head; temp != null; temp = temp.next) {\r\n System.out.print(temp.data + \" \");\r\n }\r\n System.out.println();\r\n }\r\n\r\n public void removeFirst() {\r\n if (size == 0) {\r\n System.out.println(\"List is empty\");\r\n } else if (size == 1) {\r\n head = tail = null;\r\n size = 0;\r\n } else {\r\n head = head.next;\r\n size--;\r\n }\r\n }\r\n\r\n public int getFirst() {\r\n if (size == 0) {\r\n System.out.println(\"List is empty\");\r\n return -1;\r\n } else {\r\n return head.data;\r\n }\r\n }\r\n\r\n public int getLast() {\r\n if (size == 0) {\r\n System.out.println(\"List is empty\");\r\n return -1;\r\n } else {\r\n return tail.data;\r\n }\r\n }\r\n\r\n public int getAt(int idx) {\r\n if (size == 0) {\r\n System.out.println(\"List is empty\");\r\n return -1;\r\n } else if (idx < 0 || idx >= size) {\r\n System.out.println(\"Invalid arguments\");\r\n return -1;\r\n } else {\r\n Node temp = head;\r\n for (int i = 0; i < idx; i++) {\r\n temp = temp.next;\r\n }\r\n return temp.data;\r\n }\r\n }\r\n\r\n public void addFirst(int val) {\r\n Node temp = new Node();\r\n temp.data = val;\r\n temp.next = head;\r\n head = temp;\r\n\r\n if (size == 0) {\r\n tail = temp;\r\n }\r\n\r\n size++;\r\n }\r\n\r\n public void addAt(int idx, int val) {\r\n if (idx < 0 || idx > size) {\r\n System.out.println(\"Invalid arguments\");\r\n } else if (idx == 0) {\r\n addFirst(val);\r\n } else if (idx == size) {\r\n addLast(val);\r\n } else {\r\n Node node = new Node();\r\n node.data = val;\r\n\r\n Node temp = head;\r\n for (int i = 0; i < idx - 1; i++) {\r\n temp = temp.next;\r\n }\r\n node.next = temp.next;\r\n\r\n temp.next = node;\r\n size++;\r\n }\r\n }\r\n\r\n public void removeLast() {\r\n if (size == 0) {\r\n System.out.println(\"List is empty\");\r\n } else if (size == 1) {\r\n head = tail = null;\r\n size = 0;\r\n } else {\r\n Node temp = head;\r\n for (int i = 0; i < size - 2; i++) {\r\n temp = temp.next;\r\n }\r\n\r\n tail = temp;\r\n tail.next = null;\r\n size--;\r\n }\r\n }\r\n\r\n public void removeAt(int idx) {\r\n if (idx < 0 || idx >= size) {\r\n System.out.println(\"Invalid arguments\");\r\n } else if (idx == 0) {\r\n removeFirst();\r\n } else if (idx == size - 1) {\r\n removeLast();\r\n } else {\r\n Node temp = head;\r\n for (int i = 0; i < idx - 1; i++) {\r\n temp = temp.next;\r\n }\r\n\r\n temp.next = temp.next.next;\r\n size--;\r\n }\r\n }\r\n\r\n private Node getNodeAt(int idx) {\r\n Node temp = head;\r\n for (int i = 0; i < idx; i++) {\r\n temp = temp.next;\r\n }\r\n return temp;\r\n }\r\n\r\n public void reverseDI() {\r\n int li = 0;\r\n int ri = size - 1;\r\n while(li < ri){\r\n Node left = getNodeAt(li);\r\n Node right = getNodeAt(ri);\r\n\r\n int temp = left.data;\r\n left.data = right.data;\r\n right.data = temp;\r\n\r\n li++;\r\n ri--;\r\n }\r\n }\r\n \r\n public void reversePI(){\r\n // write your code here\r\n }\r\n }\r\n\r\n public static void main(String[] args) throws Exception {\r\n BufferedReader br = new BufferedReader(new InputStreamReader(System.in));\r\n LinkedList list = new LinkedList();\r\n\r\n String str = br.readLine();\r\n while (str.equals(\"quit\") == false) {\r\n if (str.startsWith(\"addLast\")) {\r\n int val = Integer.parseInt(str.split(\" \")[1]);\r\n list.addLast(val);\r\n } else if (str.startsWith(\"size\")) {\r\n System.out.println(list.size());\r\n } else if (str.startsWith(\"display\")) {\r\n list.display();\r\n } else if (str.startsWith(\"removeFirst\")) {\r\n list.removeFirst();\r\n } else if (str.startsWith(\"getFirst\")) {\r\n int val = list.getFirst();\r\n if (val != -1) {\r\n System.out.println(val);\r\n }\r\n } else if (str.startsWith(\"getLast\")) {\r\n int val = list.getLast();\r\n if (val != -1) {\r\n System.out.println(val);\r\n }\r\n } else if (str.startsWith(\"getAt\")) {\r\n int idx = Integer.parseInt(str.split(\" \")[1]);\r\n int val = list.getAt(idx);\r\n if (val != -1) {\r\n System.out.println(val);\r\n }\r\n } else if (str.startsWith(\"addFirst\")) {\r\n int val = Integer.parseInt(str.split(\" \")[1]);\r\n list.addFirst(val);\r\n } else if (str.startsWith(\"addAt\")) {\r\n int idx = Integer.parseInt(str.split(\" \")[1]);\r\n int val = Integer.parseInt(str.split(\" \")[2]);\r\n list.addAt(idx, val);\r\n } else if (str.startsWith(\"removeLast\")) {\r\n list.removeLast();\r\n } else if (str.startsWith(\"removeAt\")) {\r\n int idx = Integer.parseInt(str.split(\" \")[1]);\r\n list.removeAt(idx);\r\n } else if(str.startsWith(\"reverseDI\")){\r\n list.reverseDI();\r\n } else if(str.startsWith(\"reversePI\")){\r\n list.reversePI();\r\n }\r\n str = br.readLine();\r\n }\r\n }\r\n}"},"python":{"code":"class Node:\n\n def __init__(self):\n self.data = 0\n self.next = None\n\n\nclass LinkedList:\n\n def __init__(self):\n self.head = None\n self.tail = None\n self.size = 0\n\n def addLast(self, val):\n temp = Node()\n temp.data = val\n temp.next = None\n\n if self.size == 0:\n self.head = self.tail = temp\n else:\n self.tail.next = temp\n self.tail = temp\n self.size += 1\n \n def getNodeAt(self, idx):\n temp = self.head\n i = 0\n while i < idx:\n temp = temp.next\n i += 1\n return temp\n \n def display(self):\n temp = self.head\n while temp is not None:\n print(temp.data, end = \" \")\n temp = temp.next\n print()\n \n def removeFirst(self):\n if self.size == 0:\n print(\"List is empty\")\n elif self.size == 1:\n self.head = self.tail = None\n self.size = 0\n else:\n self.head = self.head.next\n self.size -= 1\n \n def getFirst(self):\n if self.size == 0:\n print(\"List is empty\")\n return -1\n else:\n return self.head.data\n\n def getLast(self):\n if self.size == 0:\n print(\"List is empty\")\n return -1\n else:\n return self.tail.data\n \n def getAt(self, idx):\n if self.size == 0:\n print(\"List is empty\")\n return -1\n elif idx < 0 or idx >= self.size:\n print(\"Invalid arguments\")\n return -1\n else:\n temp = self.head\n i = 0\n while i < idx:\n temp = temp.next\n i += 1\n return temp.data\n \n def addFirst(self, val):\n temp = Node()\n temp.data = val\n temp.next = self.head\n self.head = temp\n\n if self.size == 0:\n self.tail = temp\n\n self.size += 1\n \n def removeAt(self, idx):\n if idx < 0 or idx >= self.size:\n print(\"Invalid arguments\")\n elif idx == 0:\n self.removeFirst()\n elif idx == self.size - 1:\n self.removeLast()\n else:\n temp = self.head\n i = 0\n while i < idx - 1:\n temp = temp.next\n i += 1\n\n temp.next = temp.next.next\n self.size -= 1\n\n def addAt(self, idx, val):\n if idx < 0 or idx > self.size:\n print(\"Invalid arguments\")\n elif idx == 0:\n self.addFirst(val)\n elif idx == self.size:\n self.addLast(val)\n else:\n node = Node()\n node.data = val\n\n temp = self.head\n i = 0\n while i < idx - 1:\n temp = temp.next\n i += 1\n node.next = temp.next\n\n temp.next = node\n self.size += 1\n \n def removeLast(self):\n if self.size == 0:\n print(\"List is empty\")\n elif self.size == 1:\n self.head = self.tail = None\n self.size = 0\n else:\n temp = self.head\n i = 0\n while i < self.size - 2:\n temp = temp.next\n i += 1\n\n self.tail = temp\n self.tail.next = None\n self.size -= 1\n \n def reverseDI(self):\n left=0\n right=self.size-1\n while(left<right):\n temp1 = self.getNodeAt(left)\n temp2 = self.getNodeAt(right)\n temp = temp1.data\n temp1.data = temp2.data\n temp2.data = temp\n left+=1\n right-=1\n \n \nl1 = LinkedList()\nwhile True:\n cmd=input().split(\" \")\n if \"addLast\" in cmd[0]:\n val=int(cmd[1])\n l1.addLast(val)\n \n elif \"getFirst\" in cmd[0]:\n ans=l1.getFirst()\n if(ans!=-1):\n print(ans)\n \n elif \"getLast\" in cmd[0]:\n ans=l1.getLast()\n if(ans!=-1):\n print(ans)\n \n elif \"getAt\" in cmd[0]:\n idx=int(cmd[1])\n ans=l1.getAt(idx)\n if(ans!=-1):\n print(ans)\n \n elif \"removeFirst\" in cmd[0]:\n l1.removeFirst()\n \n elif \"removeLast\" in cmd[0]:\n l1.removeLast()\n \n elif \"addFirst\" in cmd[0]:\n val=int(cmd[1])\n l1.addFirst(val)\n \n elif \"quit\" in cmd[0]:\n break\n \n elif \"display\" in cmd[0]:\n l1.display()\n \n elif \"size\" in cmd[0]:\n print(l1.size)\n \n elif \"addAt\" in cmd[0]:\n idx=int(cmd[1])\n val=int(cmd[2])\n l1.addAt(idx,val)\n \n elif \"removeAt\" in cmd[0]:\n idx=int(cmd[1])\n l1.removeAt(idx)\n \n elif \"reverseDI\" in cmd[0]:\n l1.reverseDI()"}},"points":10,"difficulty":"easy","sampleInput":"addFirst 10\r\naddFirst 20\r\naddLast 30\r\naddLast 40\r\naddLast 50\r\naddFirst 60\r\nremoveAt 2\r\ndisplay\r\nreversePI\r\ndisplay\r\nquit","sampleOutput":"60 20 30 40 50 \r\n50 40 30 20 60 \r\n","questionVideo":"https://www.youtube.com/embed/iAEvqhaeD88","hints":[],"associated":[],"solutionSeen":false,"tags":[],"meta":{"path":[{"id":0,"name":"home"},{"id":"0c54b191-7b99-4f2c-acb3-e7f2ec748b2a","name":"Data Structures and Algorithms","slug":"data-structures-and-algorithms","type":0},{"id":"91027ef1-2784-45bf-8143-cc6af4560105","name":"Linked Lists For Beginners","slug":"linked-lists-for-beginners","type":0},{"id":"43b3c352-ebd9-4520-a2f8-991fd5a7d142","name":"Reverse Linked List (pointer Iterative)","slug":"reverse-linked-list-pointer-iterative","type":1}],"next":{"id":"eaf6c6b6-5167-4d95-b183-08c2c5deb5bd","name":"Reverse Linked List (pointer Iterative)","type":3,"slug":"reverse-linked-list-pointer-iterative"},"prev":{"id":"610b62ff-d616-4f1e-a82a-5a3afb81cd74","name":"Reverse A Linked List (data Iterative)","type":3,"slug":"reverse-a-linked-list-data-iterative"}}}
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Reverse Linked List (pointer Iterative)

easy

1. You are given a partially written LinkedList class. 2. Here is a list of existing functions: 2.1 addLast - adds a new element with given value to the end of Linked List 2.2. display - Prints the elements of linked list from front to end in a single line. All elements are separated by space 2.3. size - Returns the number of elements in the linked list. 2.4. removeFirst - Removes the first element from Linked List. 2.5. getFirst - Returns the data of first element. 2.6. getLast - Returns the data of last element. 2.7. getAt - Returns the data of element available at the index passed. 2.8. addFirst - adds a new element with given value in front of linked list. 2.9. addAt - adds a new element at a given index. 2.10. removeLast - removes the last element of linked list. 2.11. removeAt - remove an element at a given index 3. You are required to complete the body of reversePI function. The function should be an iterative function and should reverse the contents of linked list by changing the "next" property of nodes. 4. Input and Output is managed for you.

Constraints

None

Format

Input

Input is managed for you

Output

Output is managed for you

Example

Sample Input

addFirst 10 addFirst 20 addLast 30 addLast 40 addLast 50 addFirst 60 removeAt 2 display reversePI display quit

Sample Output

60 20 30 40 50 50 40 30 20 60

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