解题思路：

等于 -1 时，直接 return -1

class Solution {public boolean isBalanced(TreeNode root) {return getHeight(root) != -1;}public int getHeight(TreeNode root) {if (root == null) return 0;int leftDepth = getHeight(root.left);if (leftDepth == -1) return -1;int rightDepth = getHeight(root.right);if (rightDepth == -1) return -1;int res;if (Math.abs(leftDepth - rightDepth) > 1) res = -1;else res = 1 + Math.max(leftDepth, rightDepth);return res;}
}