題目：https://www.patest.cn/contests/pat-a-PRactise/1063

代碼：

#include<cstdio>  #include<cstring>  #include<cstdlib> #include<cmath>#include<set>#include<algorithm>  using namespace std; set<int> s[55];void compare(int a,int b){	int total = s[b].size(),same=0;	for(set<int>::iterator i=s[a].begin();i!=s[a].end();i++){		if(s[b].find(*i) !=s[b].end()) same++;		else total ++;	}	printf("%.1f%/n",same*100.0/total);}int main()  {   	int n,a,b,k,t,qe;	scanf("%d",&n);	for(int i=1;i<=n;i++){	  scanf("%d",&k);	  for(int j=0;j<k;j++){	     scanf("%d",&t);		 s[i].insert(t);	  }	}	scanf("%d",&qe);	for(int i=0;i<qe;i++){	   scanf("%d%d",&a,&b);	   compare(a,b);	}    system("pause");  }