PAT 1064 朋友数 （20 分）

#include<iostream>
#include<string>
#include<map>
using namespace std;
int main() {
    int n, sum;
    map<int, int> m;
    string str;
    cin >> n;
    while (n--) {
        sum = 0;
        cin >> str;
        for (int i = 0; i < str.length(); i++)
            sum += str[i] - '0';
        m[sum]++;
    }
    cout << m.size() << endl;
    for(auto it = m.begin(); it != m.end(); it++) {
        if(it != m.begin()) cout<<" ";
        cout << it->first;
    }
    return 0;
}