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.

class Solution {
public:
    bool isBalanced(TreeNode *root) {
        return helper(root)>=0;
    }
   
    int helper(TreeNode *root)
    {
        if (root==NULL) return 0;
       
        int left = helper(root->left);
        int right = helper(root->right);
       
        if (left<0||right<0||abs(left-right)>1) return -1;  //Pay attention to
        else
        return max(left, right)+1;           
    }
};

Pseudo code to write this in an iterative solution.