[LeetCode] HouseRobber

You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed, the only constraint stopping you from robbing each of them is that adjacent houses have 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 representing the amount of money of each house, determine the maximum amount of money you can rob tonight without alerting the police.

Credits:

Special thanks to @ifanchu for adding this problem and creating all test cases. Also thanks to @ts for adding additional test cases.

1. DP問題，在每個index i有兩個選擇：如果搶劫i，則最大收益爲(不搶劫i-1)＋val［i］；如果不搶劫i，則最大收益爲（搶劫i-1）

class Solution {
public:
    int rob(vector<int>& nums) {
        int rob_true=0;
        int rob_false=0;
        for(auto val: nums)
        {
            int tmp=rob_true;
            //if rob this house, definitely cannot rob the previous house
            rob_true = rob_false + val;
            //if not rob this house, either rob or skip the previous house
            rob_false = max(tmp,rob_false);
        }
        return max(rob_true, rob_false);
    }
};

2. 遞歸的思路，超時！！！！！

class Solution {
public:
    void helper(vector<int>& nums, int start, int end, int& maxval, int tmpsum)
    {
        if(start>end) return;
        if(start==end){
            tmpsum+=nums[start];
            if(maxval<tmpsum) maxval=tmpsum;
            return;
        }
        //recursively call helper for conditions: (1) if nums[start] is picked;
        //(2) nums[start] is not picked
        helper(nums,start+2,end,maxval,tmpsum+nums[start]);
        helper(nums,start+1,end,maxval,tmpsum); //nums[start] is not picked
    }
    int rob(vector<int>& nums) {
        int maxval=0, tmpsum=0;
        helper(nums,0,nums.size()-1,maxval, tmpsum);
        return maxval;
    }
};