1#include <iostream>
2#include <vector>
3using namespace std;
4
5vector<int> maxSumOfThreeSubarrays(vector<int>& nums, int k) {
6    int n = nums.size();
7    vector<int> prefix(n + 1, 0);
8    for (int i = 0; i < n; i++) {
9        prefix[i + 1] = prefix[i] + nums[i];
10    }
11    vector<int> left(n, 0), right(n, n - k);
12    for (int i = k, total = prefix[k] - prefix[0]; i < n; i++) {
13        if (prefix[i + 1] - prefix[i + 1 - k] > total) {
14            left[i] = i + 1 - k;
15            total = prefix[i + 1] - prefix[i + 1 - k];
16        } else {
17            left[i] = left[i - 1];
18        }
19    }
20    for (int i = n - k - 1, total = prefix[n] - prefix[n - k]; i >= 0; i--) {
21        if (prefix[i + k] - prefix[i] >= total) {
22            right[i] = i;
23            total = prefix[i + k] - prefix[i];
24        } else {
25            right[i] = right[i + 1];
26        }
27    }
28    vector<int> ans(3, 0);
29    int max_sum = 0;
30    for (int i = k; i <= n - 2 * k; ++i) {
31        int l = left[i - 1], r = right[i + k];
32        int current_sum = prefix[l + k] - prefix[l] + prefix[i + k] - prefix[i] + prefix[r + k] - prefix[r];
33        if (current_sum > max_sum) {
34            max_sum = current_sum;
35            ans = {l, i, r};
36        }
37    }
38    return ans;
39}
40
41int main() {
42    vector<int> nums = {1, 2, 1, 2, 6, 7, 5, 1};
43    int k = 2;
44    vector<int> result = maxSumOfThreeSubarrays(nums, k);
45    for (int i : result) {
46        cout << i << " ";
47    }
48    return 0;
49}

1
public class Solution {
    public int[] MaxSumOfThreeSubarraysDP(int[] nums, int k) {
        int n = nums.Length;
        int[] prefix = new int[n + 1];
        int[] dp = new int[n];
        int[] left = new int[n];
        int[] right = new int[n];

        for (int i = 0; i < n; ++i) {
            prefix[i + 1] = prefix[i] + nums[i];
        }

        for (int i = k; i < n; ++i) {
            if (prefix[i + 1] - prefix[i + 1 - k] > (dp[i - 1] if i - 1 >= 0 else 0)) {
                dp[i] = prefix[i + 1] - prefix[i + 1 - k];
                left[i] = i + 1 - k;
            } else {
                dp[i] = dp[i - 1];
                left[i] = left[i - 1];
            }
        }

        right[n - k] = n - k;
        for (int i = n - k - 1; i >= 0; --i) {
            if (prefix[i + k] - prefix[i] >= prefix[right[i + 1] + k] - prefix[right[i + 1]]) {
                right[i] = i;
            } else {
                right[i] = right[i + 1];
            }
        }

        int maxSum = 0;
        int[] result = new int[3];
        for (int i = k; i <= n - 2 * k; ++i) {
            int l = left[i - 1];
            int r = right[i + k];
            int totalSum = (prefix[i + k] - prefix[i]) + (prefix[l + k] - prefix[l]) + (prefix[r + k] - prefix[r]);
            if (totalSum > maxSum) {
                maxSum = totalSum;
                result[0] = l;
                result[1] = i;
                result[2] = r;
            }
        }
        return result;
    }

    public static void Main(string[] args) {
        Solution solution = new Solution();
        int[] nums = {1, 2, 1, 2, 6, 7, 5, 1};
        int k = 2;
        int[] result = solution.MaxSumOfThreeSubarraysDP(nums, k);
        Console.WriteLine(string.Join(", ", result));
    }
}