Leetcode House Robber III

题意：House Robber 的衍生题，将房子的排列由直线改成了二叉树。

思路：DFS，在此基础上运用DP。

/**
 * 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:
    int rob(TreeNode* root) {
        pair<int, int> re;
        re = dfs(root);
        return re.first;
    }
    
    pair<int, int> dfs(TreeNode* root) {
        pair<int, int> ret;
        ret.first = 0;
        ret.second = 0;
        if(root == NULL) return ret;
        
        pair<int, int> p1;
        pair<int, int> p2;
        p1 = dfs(root->left);
        p2 = dfs(root->right);
        
        ret.first = root->val + p1.second + p2.second;
        ret.second = p1.first + p2.first;
        if(ret.second > ret.first) ret.first = ret.second;
        
        return ret;
    }
};