【算法练习】CSP--202112-1--序列查询

#include <iostream>
#include <vector>
#include <map>
#include <algorithm>
#include <iterator>
#define ll long long
using namespace std;

int n, N, sum;

int main() {
	cin >> n >> N;
	vector<ll>A(n + 2, 0);
	A[n + 1] = N;

	for (size_t i = 1; i <= n; i++)
	{
		cin >> A[i];
	}

	for (size_t i = 0; i < n + 1; i++)
	{
		sum += (A[i + 1] - A[i]) * i;
	}

	cout << sum;
	return 0;
}