`{"id":"39497525-bb6d-4d03-ada6-d696b8eb1eee","name":"Is A Binary Search Tree","description":"1. You are given a partially written BinaryTree class.\r\n2. You are required to check if the tree is a Binary Search Tree (BST) as well. In a BST every node has a value greater than all nodes on it's left side and smaller value than all node on it's right side.\r\n3. Input is managed for you. \r\n\r\nNote -> Please refer the question video for clarity.","inputFormat":"Input is managed for you.","outputFormat":"true if the tree is a BST, false otherwise","constraints":"Time complexity must be O(n)\r\nSpace should not be more than required for recursion (call-stack)","sampleCode":{"cpp":{"code":"#include <iostream>\n#include <vector>\n#include <bits/stdc++.h>\n\nusing namespace std;\n\nclass Node\n{\npublic:\n int data=0;\n Node *left = nullptr;\n Node *right = nullptr;\n Node(int data)\n {\n this->data = data;\n }\n};\n\n class Pair {\n public:\n Node *node=nullptr;\n int state=0;\n\n Pair(Node *node, int state) {\n this->node = node;\n this->state = state;\n }\n };\n\nint idx = 0;\nNode *constructTree(vector<int> &arr)\n{\n\n if (idx == arr.size() || arr[idx] == -1)\n {\n idx++;\n return nullptr;\n }\n Node *node = new Node(arr[idx++]);\n node->left = constructTree(arr);\n node->right = constructTree(arr);\n return node;\n}\n\n//Display function\nvoid display(Node *node)\n{\n if (node == nullptr)\n return;\n string str = \"\";\n str += node->left != nullptr ? to_string(node->left->data) : \".\";\n str += \" <- \" + to_string(node->data) + \" -> \";\n str += node->right != nullptr ? to_string(node->right->data) : \".\";\n cout << str << endl;\n\n display(node->left);\n display(node->right);\n}\n\n\n//Height function\nint height(Node *node)\n{\n return node == nullptr ? -1 : max(height(node->left), height(node->right)) + 1; \n}\n\n bst Bst(Node *node){\n // write your code here \n }\n\nint main(){\n int n;\n cin>>n;\n \n vector<int> arr(n,0);\n for(int i = 0; i < n; i++) {\n string tmp;\n cin>>tmp;\n if (tmp==\"n\") {\n arr[i] = -1;\n } else {\n arr[i] = stoi(tmp);\n }\n }\n \n \n Node *root = constructTree(arr);\n\n bst r = Bst(root);\n if(r.isbst == 1)\n cout << \"true\";\n else \n cout<<\"false\";\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 left;\r\n Node right;\r\n\r\n Node(int data, Node left, Node right) {\r\n this.data = data;\r\n this.left = left;\r\n this.right = right;\r\n }\r\n }\r\n\r\n public static class Pair {\r\n Node node;\r\n int state;\r\n\r\n Pair(Node node, int state) {\r\n this.node = node;\r\n this.state = state;\r\n }\r\n }\r\n\r\n public static Node construct(Integer[] arr) {\r\n Node root = new Node(arr[0], null, null);\r\n Pair rtp = new Pair(root, 1);\r\n\r\n Stack<Pair> st = new Stack<>();\r\n st.push(rtp);\r\n\r\n int idx = 0;\r\n while (st.size() > 0) {\r\n Pair top = st.peek();\r\n if (top.state == 1) {\r\n idx++;\r\n if (arr[idx] != null) {\r\n top.node.left = new Node(arr[idx], null, null);\r\n Pair lp = new Pair(top.node.left, 1);\r\n st.push(lp);\r\n } else {\r\n top.node.left = null;\r\n }\r\n\r\n top.state++;\r\n } else if (top.state == 2) {\r\n idx++;\r\n if (arr[idx] != null) {\r\n top.node.right = new Node(arr[idx], null, null);\r\n Pair rp = new Pair(top.node.right, 1);\r\n st.push(rp);\r\n } else {\r\n top.node.right = null;\r\n }\r\n\r\n top.state++;\r\n } else {\r\n st.pop();\r\n }\r\n }\r\n\r\n return root;\r\n }\r\n\r\n public static void display(Node node) {\r\n if (node == null) {\r\n return;\r\n }\r\n\r\n String str = \"\";\r\n str += node.left == null ? \".\" : node.left.data + \"\";\r\n str += \" <- \" + node.data + \" -> \";\r\n str += node.right == null ? \".\" : node.right.data + \"\";\r\n System.out.println(str);\r\n\r\n display(node.left);\r\n display(node.right);\r\n }\r\n\r\n public static int height(Node node) {\r\n if (node == null) {\r\n return -1;\r\n }\r\n\r\n int lh = height(node.left);\r\n int rh = height(node.right);\r\n\r\n int th = Math.max(lh, rh) + 1;\r\n return th;\r\n }\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 int n = Integer.parseInt(br.readLine());\r\n Integer[] arr = new Integer[n];\r\n String[] values = br.readLine().split(\" \");\r\n for (int i = 0; i < n; i++) {\r\n if (values[i].equals(\"n\") == false) {\r\n arr[i] = Integer.parseInt(values[i]);\r\n } else {\r\n arr[i] = null;\r\n }\r\n }\r\n\r\n Node root = construct(arr);\r\n \r\n // write your code here\r\n }\r\n\r\n}"},"python":{"code":"import math\nclass Node:\n \n def __init__(self,data,left,right):\n self.data = data\n self.left = None\n self.right = None\nclass Pair:\n def __init__(self,node,state):\n self.node = node\n self.state = state\n\ndef construct(arr):\n root=Node(arr[0],None,None)\n rtp=Pair(root,1);\n \n st=[]\n st.append(rtp);\n \n idx=0;\n n = len(arr)\n while(len(st)>0):\n top=st[-1];\n if top.state==1:\n idx+=1\n st[-1].state+=1\n if(arr[idx]!=-1):\n top.node.left = Node(arr[idx], None, None);\n lp = Pair(top.node.left, 1);\n st.append(lp);\n else:\n top.node.left=None;\n elif top.state==2:\n idx+=1\n st[-1].state+=1\n if(arr[idx]!=-1):\n top.node.right = Node(arr[idx], None, None);\n rp = Pair(top.node.right, 1);\n st.append(rp);\n else:\n top.node.right=None;\n else:\n st.pop()\n return root;\n\ndef height(node):\n if(node == None):\n return -1\n else:\n ans = max(height(node.left),height(node.right))+1\n return ans\n \n \ndef Bst(node):\n # write your code here\n \n \n\nn = int(input())\nst = input()\narr = [0]*n\narr = list(map(int,st.replace(\"n\",\"-1\").split(\" \")));\n\nans=bst()\n\nroot = construct(arr)\nans = Bst(root)\n\nif(ans.isbst==True):\n print(\"true\")\nelif(ans.isbst == False):\n print(\"false\")"}},"points":10,"difficulty":"easy","sampleInput":"15\r\n50 25 12 n n 37 n n 75 62 n n 87 n n","sampleOutput":"true","questionVideo":"https://www.youtube.com/embed/MLWawOETrF8","hints":[],"associated":[{"id":"1c710eff-b30b-4344-a809-51a02c95d5cd","name":"What is the time complexity of \"Is a Binary search tree\"?","slug":"what-is-the-time-complexity-of-is-a-binary-search-tree","type":4},{"id":"38aa4e9b-02cd-4ad2-9c1c-0aec6d981be8","name":"What is the space complexity of \"Is a Binary search tree\"?","slug":"what-is-the-space-complexity-of-is-a-binary-search-tree","type":4},{"id":"d81a3a51-7dbd-47ce-8ed4-8b1fe35dc7c9","name":"Which side of a node holds the values smaller than the value in current node in BST?","slug":"which-side-of-a-node-holds-the-values-smaller-than-the-value-in-current-node-in-bst","type":4},{"id":"f8c778bb-1071-4088-8b87-ede1b1ef6401","name":"What is the one extra property that makes a Binary Tree a BST?","slug":"what-is-the-one-extra-property-that-makes-a-binary-tree-a-bst","type":4}],"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":"b042fe97-356f-41ed-80fd-abacd61fc234","name":"Binary Tree For Beginners","slug":"binary-tree-for-beginners","type":0},{"id":"325811d6-1fd2-4358-9fa0-1adc346899ea","name":"Is A Binary Search Tree","slug":"is-a-binary-search-tree","type":1}],"next":{"id":"0dc469c8-b7f3-4383-987e-3e5ab36dec82","name":"Is a Binary Search Tree","type":3,"slug":"is-a-binary-search-tree"},"prev":{"id":"b3289da2-e27c-4fb2-8313-95716c574559","name":"Tilt of a Binary Tree","type":3,"slug":"tilt-of-a-binary-tree"}}}`

# Is A Binary Search Tree

1. You are given a partially written BinaryTree class. 2. You are required to check if the tree is a Binary Search Tree (BST) as well. In a BST every node has a value greater than all nodes on it's left side and smaller value than all node on it's right side. 3. Input is managed for you. Note -> Please refer the question video for clarity.

`{"id":"39497525-bb6d-4d03-ada6-d696b8eb1eee","name":"Is A Binary Search Tree","description":"1. You are given a partially written BinaryTree class.\r\n2. You are required to check if the tree is a Binary Search Tree (BST) as well. In a BST every node has a value greater than all nodes on it's left side and smaller value than all node on it's right side.\r\n3. Input is managed for you. \r\n\r\nNote -> Please refer the question video for clarity.","inputFormat":"Input is managed for you.","outputFormat":"true if the tree is a BST, false otherwise","constraints":"Time complexity must be O(n)\r\nSpace should not be more than required for recursion (call-stack)","sampleCode":{"cpp":{"code":"#include <iostream>\n#include <vector>\n#include <bits/stdc++.h>\n\nusing namespace std;\n\nclass Node\n{\npublic:\n int data=0;\n Node *left = nullptr;\n Node *right = nullptr;\n Node(int data)\n {\n this->data = data;\n }\n};\n\n class Pair {\n public:\n Node *node=nullptr;\n int state=0;\n\n Pair(Node *node, int state) {\n this->node = node;\n this->state = state;\n }\n };\n\nint idx = 0;\nNode *constructTree(vector<int> &arr)\n{\n\n if (idx == arr.size() || arr[idx] == -1)\n {\n idx++;\n return nullptr;\n }\n Node *node = new Node(arr[idx++]);\n node->left = constructTree(arr);\n node->right = constructTree(arr);\n return node;\n}\n\n//Display function\nvoid display(Node *node)\n{\n if (node == nullptr)\n return;\n string str = \"\";\n str += node->left != nullptr ? to_string(node->left->data) : \".\";\n str += \" <- \" + to_string(node->data) + \" -> \";\n str += node->right != nullptr ? to_string(node->right->data) : \".\";\n cout << str << endl;\n\n display(node->left);\n display(node->right);\n}\n\n\n//Height function\nint height(Node *node)\n{\n return node == nullptr ? -1 : max(height(node->left), height(node->right)) + 1; \n}\n\n bst Bst(Node *node){\n // write your code here \n }\n\nint main(){\n int n;\n cin>>n;\n \n vector<int> arr(n,0);\n for(int i = 0; i < n; i++) {\n string tmp;\n cin>>tmp;\n if (tmp==\"n\") {\n arr[i] = -1;\n } else {\n arr[i] = stoi(tmp);\n }\n }\n \n \n Node *root = constructTree(arr);\n\n bst r = Bst(root);\n if(r.isbst == 1)\n cout << \"true\";\n else \n cout<<\"false\";\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 left;\r\n Node right;\r\n\r\n Node(int data, Node left, Node right) {\r\n this.data = data;\r\n this.left = left;\r\n this.right = right;\r\n }\r\n }\r\n\r\n public static class Pair {\r\n Node node;\r\n int state;\r\n\r\n Pair(Node node, int state) {\r\n this.node = node;\r\n this.state = state;\r\n }\r\n }\r\n\r\n public static Node construct(Integer[] arr) {\r\n Node root = new Node(arr[0], null, null);\r\n Pair rtp = new Pair(root, 1);\r\n\r\n Stack<Pair> st = new Stack<>();\r\n st.push(rtp);\r\n\r\n int idx = 0;\r\n while (st.size() > 0) {\r\n Pair top = st.peek();\r\n if (top.state == 1) {\r\n idx++;\r\n if (arr[idx] != null) {\r\n top.node.left = new Node(arr[idx], null, null);\r\n Pair lp = new Pair(top.node.left, 1);\r\n st.push(lp);\r\n } else {\r\n top.node.left = null;\r\n }\r\n\r\n top.state++;\r\n } else if (top.state == 2) {\r\n idx++;\r\n if (arr[idx] != null) {\r\n top.node.right = new Node(arr[idx], null, null);\r\n Pair rp = new Pair(top.node.right, 1);\r\n st.push(rp);\r\n } else {\r\n top.node.right = null;\r\n }\r\n\r\n top.state++;\r\n } else {\r\n st.pop();\r\n }\r\n }\r\n\r\n return root;\r\n }\r\n\r\n public static void display(Node node) {\r\n if (node == null) {\r\n return;\r\n }\r\n\r\n String str = \"\";\r\n str += node.left == null ? \".\" : node.left.data + \"\";\r\n str += \" <- \" + node.data + \" -> \";\r\n str += node.right == null ? \".\" : node.right.data + \"\";\r\n System.out.println(str);\r\n\r\n display(node.left);\r\n display(node.right);\r\n }\r\n\r\n public static int height(Node node) {\r\n if (node == null) {\r\n return -1;\r\n }\r\n\r\n int lh = height(node.left);\r\n int rh = height(node.right);\r\n\r\n int th = Math.max(lh, rh) + 1;\r\n return th;\r\n }\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 int n = Integer.parseInt(br.readLine());\r\n Integer[] arr = new Integer[n];\r\n String[] values = br.readLine().split(\" \");\r\n for (int i = 0; i < n; i++) {\r\n if (values[i].equals(\"n\") == false) {\r\n arr[i] = Integer.parseInt(values[i]);\r\n } else {\r\n arr[i] = null;\r\n }\r\n }\r\n\r\n Node root = construct(arr);\r\n \r\n // write your code here\r\n }\r\n\r\n}"},"python":{"code":"import math\nclass Node:\n \n def __init__(self,data,left,right):\n self.data = data\n self.left = None\n self.right = None\nclass Pair:\n def __init__(self,node,state):\n self.node = node\n self.state = state\n\ndef construct(arr):\n root=Node(arr[0],None,None)\n rtp=Pair(root,1);\n \n st=[]\n st.append(rtp);\n \n idx=0;\n n = len(arr)\n while(len(st)>0):\n top=st[-1];\n if top.state==1:\n idx+=1\n st[-1].state+=1\n if(arr[idx]!=-1):\n top.node.left = Node(arr[idx], None, None);\n lp = Pair(top.node.left, 1);\n st.append(lp);\n else:\n top.node.left=None;\n elif top.state==2:\n idx+=1\n st[-1].state+=1\n if(arr[idx]!=-1):\n top.node.right = Node(arr[idx], None, None);\n rp = Pair(top.node.right, 1);\n st.append(rp);\n else:\n top.node.right=None;\n else:\n st.pop()\n return root;\n\ndef height(node):\n if(node == None):\n return -1\n else:\n ans = max(height(node.left),height(node.right))+1\n return ans\n \n \ndef Bst(node):\n # write your code here\n \n \n\nn = int(input())\nst = input()\narr = [0]*n\narr = list(map(int,st.replace(\"n\",\"-1\").split(\" \")));\n\nans=bst()\n\nroot = construct(arr)\nans = Bst(root)\n\nif(ans.isbst==True):\n print(\"true\")\nelif(ans.isbst == False):\n print(\"false\")"}},"points":10,"difficulty":"easy","sampleInput":"15\r\n50 25 12 n n 37 n n 75 62 n n 87 n n","sampleOutput":"true","questionVideo":"https://www.youtube.com/embed/MLWawOETrF8","hints":[],"associated":[{"id":"1c710eff-b30b-4344-a809-51a02c95d5cd","name":"What is the time complexity of \"Is a Binary search tree\"?","slug":"what-is-the-time-complexity-of-is-a-binary-search-tree","type":4},{"id":"38aa4e9b-02cd-4ad2-9c1c-0aec6d981be8","name":"What is the space complexity of \"Is a Binary search tree\"?","slug":"what-is-the-space-complexity-of-is-a-binary-search-tree","type":4},{"id":"d81a3a51-7dbd-47ce-8ed4-8b1fe35dc7c9","name":"Which side of a node holds the values smaller than the value in current node in BST?","slug":"which-side-of-a-node-holds-the-values-smaller-than-the-value-in-current-node-in-bst","type":4},{"id":"f8c778bb-1071-4088-8b87-ede1b1ef6401","name":"What is the one extra property that makes a Binary Tree a BST?","slug":"what-is-the-one-extra-property-that-makes-a-binary-tree-a-bst","type":4}],"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":"b042fe97-356f-41ed-80fd-abacd61fc234","name":"Binary Tree For Beginners","slug":"binary-tree-for-beginners","type":0},{"id":"325811d6-1fd2-4358-9fa0-1adc346899ea","name":"Is A Binary Search Tree","slug":"is-a-binary-search-tree","type":1}],"next":{"id":"0dc469c8-b7f3-4383-987e-3e5ab36dec82","name":"Is a Binary Search Tree","type":3,"slug":"is-a-binary-search-tree"},"prev":{"id":"b3289da2-e27c-4fb2-8313-95716c574559","name":"Tilt of a Binary Tree","type":3,"slug":"tilt-of-a-binary-tree"}}}`

Editor

# Is A Binary Search Tree

easy

1. You are given a partially written BinaryTree class. 2. You are required to check if the tree is a Binary Search Tree (BST) as well. In a BST every node has a value greater than all nodes on it's left side and smaller value than all node on it's right side. 3. Input is managed for you. Note -> Please refer the question video for clarity.

## Constraints

Time complexity must be O(n) Space should not be more than required for recursion (call-stack)

## Format

### Input

Input is managed for you.

### Output

true if the tree is a BST, false otherwise

## Example

Sample Input

```.css-23h8hz{color:inherit;font-size:0.875rem;line-height:1.125rem;letter-spacing:0.016rem;font-weight:var(--chakra-fontWeights-normal);white-space:pre-wrap;}15 50 25 12 n n 37 n n 75 62 n n 87 n n```

### Sample Output

`.css-3oaykw{color:var(--chakra-colors-active-primary);font-size:0.875rem;line-height:1.125rem;letter-spacing:0.016rem;font-weight:var(--chakra-fontWeights-normal);white-space:pre-wrap;font-family:Monospace;}true`

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