LeetCode: Balanced Binary Tree

Problem:

Given a binary tree, determine if it is height-balanced.



An example of a height-balanced tree. A height-balanced tree is a tree whose subtrees differ in height by no more than one and the subtrees are height-balanced, too.
先提供一种递归解法，复杂度较高。

/**
* Definition for binary tree
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
int maxHeight(TreeNode *root) {
if (root == NULL) return 0;

int left = maxHeight(root->left) + 1;
int right = maxHeight(root->right) + 1;
return left > right ? left : right;
}

bool isBalanced(TreeNode *root) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
if (root == NULL) return true;

while(root != NULL)
{
int left = maxHeight(root->left);
int right = maxHeight(root->right);
if (abs(left - right) >= 2)
return false;
else
return isBalanced(root->left) && isBalanced(root->right);
}
}
};