Valid Binary Search Tree

Problem TC: O(n), SC: O(n) /** * 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; * } * } */ class Solution { public boolean isValidBST(TreeNode root) { return isValid(root,-1001,1001); } // inorder dfs public boolean isValid(TreeNode root,int l, int r){ if(root ==null) return true; boolean left = isValid(root.left,l,root.val); //root.val should always be greater than its left child value and less that its right chil value if(root.val =r) return false; boolean right = isValid(root.right,root.val, r); return left && right; } }

Mar 19, 2025 - 18:35

TC: O(n), SC: O(n)

/**
 * 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;
 *     }
 * }
 */

class Solution {
    public boolean isValidBST(TreeNode root) {
        return isValid(root,-1001,1001);
    }
    // inorder dfs
    public boolean isValid(TreeNode root,int l, int r){
        if(root ==null) return true;
        boolean left = isValid(root.left,l,root.val);
        //root.val should always be greater than its left child value and less  that its right chil value
        if(root.val <=l || root.val>=r) return false;
        boolean right = isValid(root.right,root.val, r);
        return left &&  right;

    }
}