leetcode 110

110. 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.

判断二叉树是否为平衡二叉树。

递归解法：
（1）如果二叉树为空，返回真
（2）如果二叉树不为空，如果左子树和右子树都是AVL树并且左子树和右子树高度相差不大于1，返回真，其他返回假

代码如下：

 /**
  * 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:
     bool isBalanced(TreeNode* root) {
         int height;
         return isAvl(root, height);
     }
     bool isAvl(TreeNode* pRoot, int & height)
     {
         if(pRoot == NULL)
         {
             height = ;
             return true;
         }
         int heightLeft;
         bool resultLeft = isAvl(pRoot->left, heightLeft);
         int heightRight;
         bool resultRight = isAvl(pRoot->right, heightRight);
         if(resultLeft && resultRight && abs(heightLeft - heightRight) <= )
         {
             height = max(heightLeft, heightRight) + ;
             return true;
         }
         else
         {
             height = max(heightLeft, heightRight) + ;
             return false;
         }
     }
 };