wayetan
1/3/2014 - 8:06 AM

Validate Binary Search Tree

Validate Binary Search Tree

/**
 * Given a binary tree, determine if it is a valid binary search tree (BST).
 * Assume a BST is defined as follows:
 *      The left subtree of a node contains only nodes with keys less than the node's key.
 *      The right subtree of a node contains only nodes with keys greater than the node's key.
 *      Both the left and right subtrees must also be binary search trees.
 */
 
 /**
 * 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) {
        if(root == null) return true;
        if(root.left == null && root.right == null) return true;
    	return isBSTUtil(root, Integer.MIN_VALUE, Integer.MAX_VALUE);
	}

	public boolean isBSTUtil(TreeNode root, int min, int max) {
		if (root == null)
			return true;
		return (root.val > min && root.val < max && isBSTUtil(root.left, min, root.val) && isBSTUtil(root.right, root.val, max));
	}
}