Balanced Binary Tree

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
private: bool OK ;
public:
    bool isBalanced(TreeNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        OK = true;
        if(root==NULL)
        return OK;
        height(root);
        return OK;
    }
    
    int height(TreeNode *root)
    {
        if(root->left==NULL&&root->right==NULL)
        {
            return 1;
        }
        int left=0,right=0;
        if(root->left!=NULL)
        {
            left = height(root->left);
        }
        if(root->right!=NULL)
        {
            right = height(root->right);
        }
        if(abs(left-right)>1)
        OK =false;
        return (left>right?left:right)+1;
    }
};