Balanced Binary Tree

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.

» Solve this problem

Complexity: O(n)

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool isBalanced(TreeNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int rootDepth = 0;
        return _isBalanced(root, rootDepth);
    }
    
    bool _isBalanced(TreeNode *root, int& depth) {
        if (!root) return true;
        
        int leftDepth = depth + 1;
        int rightDepth = depth + 1;
        bool subTreeResult = _isBalanced(root->left, leftDepth)
            && _isBalanced(root->right, rightDepth);
            //trigger recursion first to avoid computation of depth
            //until we reach the leaf node
        
        depth = max(leftDepth, rightDepth);
           //recursively update parent depth, bottom-up 
        if (subTreeResult && abs(leftDepth - rightDepth) <= 1) {
            return true;
        }
        else {
            return false;
        }
    }
};