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ValidateBinarySearchTree.java
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ValidateBinarySearchTree.java
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package com.leetcode;
public class ValidateBinarySearchTree {
//https://leetcode.com/problems/validate-binary-search-tree/
class Solution {
public boolean isValidBST(TreeNode root) {
if(root == null)
return true;
return isValidBSTHelper(root,null,null);//passing null is better than int max and int low as it will fail if node is equal to max or min . Also edge case has int.max_values
}
public boolean isValidBSTHelper(TreeNode root, Integer lower , Integer upper) {
if(root == null)
return true;
int val = root.val;
if(null != lower && lower >= val)
return false;
if(null != upper && upper <= val)
return false;
return isValidBSTHelper(root.left,lower,val) && isValidBSTHelper(root.right,val,upper);
}
}
//Definition for a binary tree node.
public class TreeNode {
int val;
TreeNode left;
TreeNode right;
TreeNode() {}
TreeNode(int val) { this.val = val; }
TreeNode(int val, TreeNode left, TreeNode right) {
this.val = val;
this.left = left;
this.right = right;
}
}
}