[110 Balanced Binary Tree] #leetcode

110_0802.java

/**
 * Definition for a binary tree node.
 * 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;
        }
        
        return Math.abs(depth(root.left) - depth(root.right)) <= 1 &&
            isBalanced(root.left) && isBalanced(root.right);
    }
    
    private int depth(TreeNode node) {
        if (node == null) {
            return 0;
        }
        
        return Math.max(depth(node.left), depth(node.right)) + 1;
    }
}

public class Solution1 {
    public boolean isBalanced(TreeNode root) {
        return depth(root) != -1;
    }
    
    private int depth(TreeNode node) {
        if (node == null) {
            return 0;
        }
        
        int left = depth(node.left);
        int right = depth(node.right);
        
        if (left == -1 || right == -1) {
            return -1;
        }
        
        if ( Math.abs(left - right) <= 1 ) {
            return Math.max(left, right) + 1;
        }
        
        return -1;
    }
}