【力扣·每日一题】689. 三个无重叠子数组的最大和 (C++ 前缀和优化dp 保存路径)

class Solution {
public:
    vector<int> maxSumOfThreeSubarrays(vector<int>& nums, int k) {
        int n=nums.size();
        int sum[n],ans=0,dp[n][5],pre[n][5];
        memset(sum,0,sizeof sum);
        memset(dp,0,sizeof dp);
        for(int i=0;i<k;i++){
           ans=ans+nums[i];
        }
        sum[k-1]=ans;
        for(int i=k;i<n;i++){
           ans=ans+nums[i]-nums[i-k];
           sum[i]=ans;
        }
        dp[k-1][1]=sum[k-1];pre[k-1][1]=k-1;
        for(int i=k;i<n;i++){
            for(int j=1;j<=3;j++){
                dp[i][j]=dp[i-1][j];//第i个不选
                pre[i][j]=pre[i-1][j];
                if(dp[i][j]<dp[i-k][j-1]+sum[i]){
                    dp[i][j]=dp[i-k][j-1]+sum[i];
                    pre[i][j]=i;
                }
            }
        }
        vector<int>res;
        int x=pre[n-1][3];
        res.push_back(x-k+1);
        for(int i=2;i>0;i--){
            x=pre[x-k][i];
            res.push_back(x-k+1);
        }
        reverse(res.begin(),res.end());
        return res;
    }
};