leetcode 110. Balanced Binary Tree

头文件在http://blog.csdn.net/charles1e/article/details/56479700

/*leetcode 110. Balanced Binary TreeGiven 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.题目大意：判断一个树是不是平衡树解题思路：1. 先求一颗树的辅助函数DepthMax()求解最大高度,然后对每一个节点，判断其左右子树是否平衡2. DFS.*/#include "TreeInclude.h"class Solution1 {public:    bool isBalanced(TreeNode* root)     {        if (root == NULL)            return true;        if (abs(DepthMax(root->left)-DepthMax(root->right)) > 1)            return false;        return isBalanced(root->left) && isBalanced(root->right);    }    int DepthMax(TreeNode* root)    {        if (root == NULL)            return 0;        return 1 + max(DepthMax(root->left), DepthMax(root->right));    }};//DFS:至下而上class Solution {private:    bool flag;public:    bool isBalanced(TreeNode* root)    {        if (!root)            return true;        flag = true;        DFS(root, 1);        return flag;    }    int DFS(TreeNode* root, int depth)    {        if (!flag)            return 0;        if (!root->left && !root->right)            return depth;        int left = depth;        int right = depth;        if (root->left)            left = DFS(root->left, depth + 1);        if (root->right)            right = DFS(root->right, depth + 1);        if (abs(left - right) > 1)            flag = false;        return max(left, right);    }};void TEST(){    Solution sol;    vector<int> v{ 3,-1,20,-1,-1,15,7 };    TreeNode* root = CreateTree(v);    cout << sol.isBalanced(root) << endl;}int main(){    TEST();    return 0;}