Submission #726633

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Source Code Expand

#include <iostream>
#include <vector>
using namespace std;
using ull = unsigned long long;

int main()
{
	int n, k;

	cin >> n >> k;

	vector<int> v;
	for (int i = 0; i < n; i++) {
		int a;
		cin >> a;
		v.emplace_back(a);
	}

	ull sum = 0;

	ull onesum = 0;
	for (int i = 0; i < n; i++) {
		onesum += v.at(i);
	}
	int zure = (((n - 1) % k) + 1);
	sum = onesum * (zure + 1);
	for (int i = 0; i < zure; i++) {
		sum -= v.at(i) * (zure - i);
		sum -= v.at(n - 1 - i) * (zure - i);
	}

	/*
	vector<int> v;
	for (int i = 0; i < n; i++) {
		int a;
		cin >> a;
		v.emplace_back(a);
	}

	if (k > n / 2) {
		k = n - k + 1;
	}

	for (int i = 0; i < k; i++) {
		for (int j = i; j < n - i; j++) {
			sum += v.at(j);
		}
	}
	*/

	/*
	if (k > n / 2) {
		k = n - k + 1;
	}

	for (int i = 1; i <= n; i++) {
		if (i < k) {
			sum += v.at(i-1) * i;
		}
		else if (i > n - k + 1) {
			sum += v.at(i-1) * (n - i + 1);
		}
		else {
			sum += v.at(i-1) * k;
		}
	}
	*/

	cout << sum;

	return 0;
}

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