LeetCode：110_Balanced Binary Tree | 平衡二叉树 | Easy

要求：判断一棵树是否是平衡二叉树

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.
 

代码如下：

struct TreeNode {
    int            val;
    TreeNode    *left;
    TreeNode    *right;
    TreeNode(int x): val(x),left(NULL), right(NULL) {}
};

int maxTreeDepth(TreeNode *root) //先求树的深度
{
    if (NULL == root)
        return 0;
    int lval = maxTreeDepth(root->left);
    int rval = maxTreeDepth(root->right);
    return 1 + (lval > rval ? lval:rval);
}
bool isBalanced(TreeNode *root)//根据树的深度再来判断是否是平衡树
{
    if(NULL == root)
        return true;
    int diff = maxTreeDepth(root->left) - maxTreeDepth(root->right);
    if (diff < -1 || diff > 1)
        return false;
    return isBalanced(root->left) && isBalanced(root->right);
}