leetcode 110. Balanced Binary Tree

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

/* leetcode 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. 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;
}