Amazon 1: check binary search tree

Write a function isBST(BinaryTree *node) to verify if a given binary tree is a Binary Search Tree (BST) or not

1. every node must be greater than left node and less than right node.

2. also must be less than parent if left child or greater than parent if right child.

java 1. (NULL null) 2. (-> .) 3. ( !treenode  treenode==null) 4. (INT_MIN Integer.MIN_VALUE) 

 

 

class Solution {
public:

    bool isBinarySearchTree(TreeNode * root ) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        return isBST( root, INT_MIN, INT_MAX);
    }
    
    bool isBST( TreeNode* root, int Min, int Max) {
        if(!root) return true;
        
        if( root->val > Min && root->val < Max) {
            return isBST( root->left, Min, root->val) && isBST( root->right, root->val, Max);
        } else {
            return false;
        }
    }
};

 

java version

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public boolean isValidBST(TreeNode root) {
        // Start typing your Java solution below
        // DO NOT write main() function
        return isValidRec(root, Integer.MIN_VALUE, Integer.MAX_VALUE); 
    }
    
    public boolean isValidRec(TreeNode root, int min, int max) {
        if( root==null ) return true;
        
        int val = root.val;
        if( val <= min || val >= max) return false;
        
        return isValidRec( root.left, min, val) && isValidRec(root.right, val, max);
        
        
    }
}