LeetCode 110. Balanced Binary Tree

https://leetcode.com/problems/balanced-binary-tree/description/

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int maxDepth(TreeNode* root, int currDepth) {
        int left_depth = (root->left == nullptr) ? currDepth : maxDepth(root->left, currDepth + 1);
        int right_depth = (root->right == nullptr) ? currDepth : maxDepth(root->right, currDepth + 1);
        if (left_depth == -1 || right_depth == -1)
            return -1;
        if (left_depth - right_depth > 1 ||
            right_depth - left_depth > 1)
            return -1;
        return max(left_depth, right_depth);
    }
    bool isBalanced(TreeNode* root) {
        if (root == nullptr)
            return true;
        if (maxDepth(root, 0) == -1)
            return false;
        return true;
    }
};