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.

思路：给定一棵树，判断这个树是不是平衡二叉树。平衡二叉树的定义如下：

（1）对于根节点root来说，其左右子树的高度差的绝对值小于等于1

（2）左子树为平衡的

（3）右子树为平衡的

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) {
if(!root)
return true;
return fabs(getTreeHeigh(root->left)-getTreeHeigh(root->right))<=1&&isBalanced(root->left)&&isBalanced(root->right);
}

int getTreeHeigh(TreeNode *root) //返回一棵树的高度是多少
{
if(root==NULL)
return 0;
return max(getTreeHeigh(root->left),getTreeHeigh(root->right))+1;
}
};