促销活动 (Hoax or what,UVa 11136)

#include <iostream>
#include <string.h>
#include <string>
#include <fstream>
#include <algorithm>
#include <stdio.h>
#include <vector>
#include <queue>
#include <set>
#include <cmath>
using namespace std;
const double eps = 1e-8;
const double pi=acos(-1.0);
const int INF=0x7fffffff;
unsigned long long uINF = ~0LL;
#define MAXN 1007
#define mod 1000000007
typedef long long LL;
multiset<int> s;
int main()
{
    int n,k;
    while(scanf("%d",&n),n!=0)
    {
        s.clear();
        int ans=0,temp;
        for(int i=0;i<n;i++)
        {
        scanf("%d",&k);
        for(int j=0;j<k;j++)
        {
            scanf("%d",&temp);
            s.insert(temp);
        }
        int minn,maxx;
        if(s.size()>0)
        {
            multiset<int>::iterator it;
            it=s.begin();minn=*it;
            it=s.end();it--;maxx=*it;
            s.erase(it);
            if(s.size()>0)
            {
                it=s.begin();
                s.erase(it);
            }
            ans+=maxx-minn;
        }
        }
        printf("%d
",ans);
    }

    return 0;
}

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