Balanced Binary Tree

/**
 * 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:
    bool isBalanced(TreeNode* root) {
        return height(root) >= 0;
    }
    
    int height(TreeNode *root)
    {
        if(!root)
            return 0;
            
        int lt = height(root->left);
        int rt = height(root->right);
        
        if(lt == -1 || rt == -1 || abs(lt-rt) > 1)
            return -1;
        
        return max(lt, rt) + 1;
    }
};