【PAT甲级A1124】 Raffle for Weibo Followers (20分)（c++）

本文链接：https://blog.youkuaiyun.com/qq_37112826/article/details/110291293

本文介绍了一个简单的抽奖程序设计案例，该程序用于从微博转发中选取幸运粉丝作为赢家，并确保每位粉丝仅能获奖一次。通过使用C++编程语言，文章详细阐述了如何利用map数据结构跟踪获奖者，并提供了一段实现这一功能的参考代码。

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1124 Raffle for Weibo Followers (20分)

作者：CHEN, Yue
单位：浙江大学
代码长度限制：16 KB
时间限制：400 ms
内存限制：64 MB

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...

题意：

抽奖，共m个人参与，第一个获奖的人在抽奖人第s位，此后每隔n为就得奖，得奖的人id不能重复，若重了那他的下一位获奖，若目前参与的人还没产生获奖的人，输出keepgoing。

思路：

用map映射来标记此人有没有获得过奖，用cnt来记录间隔人数，当此人没获得过奖且下标等于起始获奖下标则输出，cnt置为0，每参与一个人cnt++，当此人没获得过奖且cnt>=间隔人数，则输出（只要那人已获奖，cnt会一直++，一旦下一个获奖了，才清空间隔计数）。

参考代码：

#include <iostream>
#include <string>
#include <unordered_map>

using namespace std;

int main() {
    int m,n,s,flag=0;
    string str;
    unordered_map<string,int> mp;
    scanf("%d%d%d",&m,&n,&s);
    for(int i=1,cnt=1000;i<=m;i++,cnt++){
        cin>>str;
        if((i==s||i>s&&cnt>=n)&&mp[str]!=1){
            mp[str]=1;
            flag=1;
            cout<<str<<endl;
            cnt=0;
        }
    }
    if(flag==0)printf("Keep going...");
    return 0;
}

如有错误，欢迎指正