Leetcode - Tree - 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.

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool isBalanced(TreeNode *root) {
        int depth;
        return checkBalanced(root, depth);
    }
    bool checkBalanced(TreeNode *root, int &depth) // 给checkBalanced传入depth是为了求depth的值，由于checkBalanced只能返回一个值，所以传入一个引用，求depth的值。
    {
        if(root==NULL)
        {
            depth=0;
            return true;
        }
        int depthLeft,depthRight;
        bool leftBalanced=checkBalanced(root->left, depthLeft);
        bool rightBalanced=checkBalanced(root->right, depthRight);
        depth=max(depthLeft+1,depthRight+1);
        return leftBalanced&&rightBalanced&&(abs(depthLeft-depthRight)<=1);
    }
};