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.

public boolean isBalanced(TreeNode root) {
if(root == null) return true;
return depth(root) == -1 ? false:true;
}
private int depth(TreeNode root) {    //返回-1代表不平衡；返回正整数代表树的最大高度
if(root == null) return 0;
int left = depth(root.left);
if(left == -1) return -1;
int right = depth(root.right);
if(right == -1) return -1;
if(right - left > 1 || right -left < -1) return -1; //左右子树不平衡
return right >= left ? right+1:left+1;
}