21. Balanced Binary Tree

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public boolean isBalanced(TreeNode root) {
        if (root==null) return true;
        if (Math.abs(maxDepth(root.left)-maxDepth(root.right))>1) return false;
        return isBalanced(root.left) && isBalanced(root.right);
    }
   
    private int maxDepth(TreeNode root) {
        if (root==null) return 0;
        return Math.max(maxDepth(root.left),maxDepth(root.right))+1;
    }
}