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:
    int treeHeight(TreeNode* root) {
        if(!root) return 0;
        
        int left_height = treeHeight(root->left);
        if(left_height == -1) return -1;
        int right_height = treeHeight(root->right);
        if(right_height == -1) return -1;
        
        if(abs(left_height-right_height) > 1) {
            return -1;
        } 
        else {
            return 1 + max(left_height, right_height);
        }
    }
    bool isBalanced(TreeNode *root) {
        return treeHeight(root) != -1;
    }
};