213. House Robber II

You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed. All houses at this place are arranged in a circle. That means the first house is the neighbor of the last one. Meanwhile, adjacent houses have a security system connected, and it will automatically contact the police if two adjacent houses were broken into on the same night.

Given a list of non-negative integers nums representing the amount of money of each house, return the maximum amount of money you can rob tonight without alerting the police.

Example 1:

Input: nums = [2,3,2]
Output: 3
Explanation: You cannot rob house 1 (money = 2) and then rob house 3 (money = 2), because they are adjacent houses.
Example 2:

Input: nums = [1,2,3,1]
Output: 4
Explanation: Rob house 1 (money = 1) and then rob house 3 (money = 3).
Total amount you can rob = 1 + 3 = 4.
Example 3:

Input: nums = [0]
Output: 0

Constraints:

1 <= nums.length <= 100
0 <= nums[i] <= 1000

class Solution {
public:
    int rob(vector<int>& nums) {
        int length = nums.size();
        if (length == 1) {
            return nums[0];
        }
        
        vector<int> result_1{0,0,0};
        for (int i=0; i<length-1; ++i) {
            int v2 = nums[i] + result_1[i-2+3];
            int v3 = nums[i] + result_1[i-3+3];
            result_1.emplace_back(std::max(v2, v3));
        }
        
        vector<int> result_2{0,0,0};
        for (int i=1; i<length; ++i) {
            int v2 = nums[i] + result_2[i-3+3];
            int v3 = nums[i] + result_2[i-4+3];
            result_2.emplace_back(std::max(v2, v3));
        }
        
        int ret = std::max({
                        result_1[length], 
                        result_1[length+1],
                        result_2[length], 
                        result_2[length+1],
                  });
            
        return ret;
    }
    
};

Runtime: 4 ms, faster than 48.77% of C++ online submissions for House Robber II.
Memory Usage: 8.4 MB, less than 5.19% of C++ online submissions for House Robber II.

一遍过，开心，但是性能一般，提升的话可以不用vector吧（用stack？），或者reserve vector（试了，没效果）