题意：训练指南P245

分析：set维护，查询删除最大最小值

#include 
     
      using namespace std;typedef long long ll;int main(void)  {    int n;    multiset
      
        S;    while (scanf ("%d", &n) == 1)   {        if (!n) break;        S.clear ();        ll ans = 0;        for (int m, i=1; i<=n; ++i)    {            scanf ("%d", &m);            for (int v, j=1; j<=m; ++j)    {                scanf ("%d", &v);                S.insert (v);            }            int p1 = *(S.begin ());            int p2 = *(S.rbegin ());            ans += p2 - p1;            S.erase (S.find (p1));            S.erase (S.find (p2));        }        printf ("%I64d\n", ans);    }    return 0;}