/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    bool isBalanced(TreeNode* root) {
        return getDepth(root) == -1? false:true;
    }
    //返回以该节点为根节点的二叉树的高度，如果不是二叉搜索树了则返回-1
    int getDepth(TreeNode *node)
    {
        if(node==nullptr)   return 0;
        int leftDepth = getDepth(node->left);
        if(leftDepth == -1)     return -1;      //左子树已经不是二叉平衡树
        int rightDepth = getDepth(node->right);
        if(rightDepth == -1)    return -1;      //右?树已经不是?叉平衡树

        int result = 0;
        //中序
        if(abs(leftDepth-rightDepth)>1)
            result = -1;
        else
        {
            result = 1 +max(leftDepth,rightDepth);  //以当前节点作为根节点的最大高度
        }
        return result;
    }
};