110. Balanced Binary Tree | 判断是否是平衡二叉树

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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/**
* 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) {
int depth = 0;
return depthTree(root) != -1;
}

public int depthTree(TreeNode root) {
if (root == null) {
return 0;
}
int left = depthTree(root.left);
if (left == -1) {
return -1;
}
int right = depthTree(root.right);
if (right == -1) {
return -1;
}

if (Math.abs(right - left) > 1) {
return -1;
}
return Math.max(left, right) + 1;
}
}