110-Balanced Binary Tree (Height Match O(n) space).cpp

/**
 * 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:
    unordered_map<TreeNode*,int> heights;
    int height(TreeNode* root)
    {
        if(!root)
            return 0;
        if(heights.count(root))
            return heights[root];
        return heights[root]=1+max(height(root->left),height(root->right));
    }
    bool isBalanced(TreeNode* root) 
    {
        if(!root)
            return true;
        int left=height(root->left),right=height(root->right);
        return abs(left-right)<=1&&isBalanced(root->left)&&isBalanced(root->right);
    }
};