PAT甲级——A1124 Raffle for Weibo Followers

John got a full mark on PAT. He was so happy that he decided to hold a raffle（抽奖） for his followers on Weibo -- that is, he would select winners from every N followers who forwarded his post, and give away gifts. Now you are supposed to help him generate the list of winners.

Input Specification:

Each input file contains one test case. For each case, the first line gives three positive integers M (≤ 1000), N and S, being the total number of forwards, the skip number of winners, and the index of the first winner (the indices start from 1). Then M lines follow, each gives the nickname (a nonempty string of no more than 20 characters, with no white space or return) of a follower who has forwarded John's post.

Note: it is possible that someone would forward more than once, but no one can win more than once. Hence if the current candidate of a winner has won before, we must skip him/her and consider the next one.

Output Specification:

For each case, print the list of winners in the same order as in the input, each nickname occupies a line. If there is no winner yet, print Keep going...instead.

Sample Input 1:

9 3 2
Imgonnawin!
PickMe
PickMeMeMeee
LookHere
Imgonnawin!
TryAgainAgain
TryAgainAgain
Imgonnawin!
TryAgainAgain

Sample Output 1:

PickMe
Imgonnawin!
TryAgainAgain

Sample Input 2:

2 3 5
Imgonnawin!
PickMe

Sample Output 2:

Keep going...

#include <iostream>
#include <unordered_map>
#include <string>
using namespace std;
int m, k, s;
int main()
{
    cin >> m >> k >> s;
    unordered_map<string,int>res;
    string str;
    for (int i = 1; i <= m; ++i)
    {
        cin >> str;
        if (i == s)
        {
            if (res[str] == 1)//输出过
                s++;//后移动
            else
            {
                cout << str << endl;
                res[str] = 1;
                s += k;
            }
        }
    }
    if (res.size() == 0)
        cout << "Keep going..." << endl;
    return 0;
}