110. Balanced Binary Tree

Given a binary tree, determine if it is height-balanced.

For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.

 

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 (E) Maximum Depth of 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 (depth(root) == -1) 
            return false;
        return true;
    }
    
    private int depth(TreeNode root) {
        if (root == null) 
            return 0;
        int left = depth(root.left);
        int right = depth(root.right);
        // If any subtree fails, all parent nodes should fail. No need to calculate depth.
        if (left == -1 || right == -1 || Math.abs(left-right) > 1) 
            return -1;
        return Math.max(left,right)+1;
    }
}