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更新至A…

题A

题意：$n$ 组camp，每组若干个人，问多少人参加了全部camp
解：略

#include<bits/stdc++.h>
using namespace std;
map<string,int> p, q;
int main(){
    int n; cin >> n;
    set<string> s;
    for(int j = 1; j <= n; ++ j){
        int c; cin >> c;
        for(int i = 1; i <= c; ++ i) {
            string x; cin >> x;
            p[x] ++;
            s.insert(x);
        }
    }
    for(auto [x, y]: p) if(y == n) q[x] ++;
    
    cout << q.size() << '\n';
    for(auto [x, y]: q) cout << x << '\n';
    
}