B1064 朋友数

题目：https://pintia.cn/problem-sets/994805260223102976/problems/994805267416334336
一遍过，注意点是set不可以使用迭代器+数字的方法索引

代码

#include<vector>
#include<set>
#include<cstdio>
using namespace std;
int main(){
    int n;
    scanf("%d", &n);
    vector<int> num(n);
    set<int> res;
    for(int i = 0; i < n; i++) scanf("%d", &num[i]);
    for(int i = 0; i < n; i++){
        int friend_num = 0;
        while(num[i] != 0){
            friend_num += num[i] % 10;
            num[i] /= 10;
        }
        res.insert(friend_num);
    }
    printf("%d\n", res.size());
    printf("%d", *res.begin());
    for(auto it = res.begin(); it != res.end(); it++){
        if(it == res.begin())continue;
        printf(" %d", *it);
    }
}