题解 100% AC

#include<bits/stdc++.h>
using namespace std;
const int N = 1e5+10;
int m, s, c, a[N], b[N]; 
bool cmp (int x, int y) {return x > y;}
int main() {
	cin >> m >> s >> c;
	for (int i=1; i<=c; i++)cin >> a[i];
	if (m>c) {
		cout << c;
		return 0;
	}
	sort(a+1, a+c+1);
	int cnt = a[c]-a[1]+1; 
	for (int i=2; i<=c; i++)b[i-1]=a[i]-a[i-1]; 
	sort(b+1, b+c, cmp);
	for (int i=1; i<m; i++)cnt = cnt-b[i]+1;
	cout << cnt;
	return 0;
}