用優先佇列存放不連續的斷點及斷的位置。優先取間距大的，在斷點斷開。

#include <iostream>
#include <cstdio>
#include <cmath>
#include <algorithm>
#include <vector>
#include <iomanip>
#include <cstring>
#include <map>
#include <queue>
#include <set>
#include <cassert>
#include 
 
<stack>
#define mkp make_pair
using namespace std;
const double EPS=1e-8;
typedef long long lon;
const lon SZ=1050,INF=0x7FFFFFFF;
lon arr[SZ],cut[SZ];

struct nd{
    int a,b;
    nd(int x,int y):a(x),b(y){}
    bool operator<(const nd &rbs)const
    {
        return a<rbs.a;
    }
};

 
int main()
{
    std::ios::sync_with_stdio(0);
    //freopen("d:\\1.txt","r",stdin);
    lon casenum;
    //cin>>casenum;
    //for(lon time=1;time<=casenum;++time)
    {
        lon k,tot,n;
        cin>>k>>tot>>n;
        priority_queue<nd> pq;
        for(int i=1;i<=n;++i)
        {
            cin
 
>>arr[i];
        }
        sort(arr+1,arr+1+n);
        for(int i=1;i<=n;++i)
        {
            if(i!=1&&arr[i]-arr[i-1]>1)
            {
                pq.push(nd(arr[i]-arr[i-1],i));
            }
        }
        for(;k!=1;)
        {
            if(pq.empty())--k;
            else
            {
                nd pos=pq.top();
                pq.pop();
                //cout<<"pos.a: "<<pos.a<<endl;
                cut[pos.b]=1;
                --k;
            }
        }
        int bg=1;
        int res=0;
        for(int i=2;i<=n;++i)
        {
            if(cut[i])
            {
                //cout<<"i: "<<i<<endl;
                res+=arr[i-1]-arr[bg]+1;
                //cout<<(arr[i-1]-arr[bg]+1)<<endl;
                bg=i;
            }
        }
        res+=arr[n]-arr[bg]+1;
        cout<<res<<endl;
    }
    return 0;
}