题目链接：https://codeforces.com/contest/1166/problem/E
题解：
代码：
#include<bits/stdc++.h> using namespace std; const int maxm = 55; set<int>st[maxm]; bool insect(int x, int y){ set<int>::iterator it; for(it = st[x].begin(); it != st[x].end(); it++){ if(st[y].count(*it)) return true; } return false; } int main(){ int m, n; cin >> m >> n; for(int i = 0; i < m; i++){ int s, a; cin >> s; while(s--){ cin >> a; st[i].insert(a); } } bool flag = true; for(int i = 0; i < m; i++){ for(int j = 0; j < m; j++){ if(i == j) continue; if(!insect(i, j)){ flag = false; break; } } } if(flag) cout << "possible\n"; else cout << "impossible\n"; return 0; }
