Shuffling Machine

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本文介绍了一种模拟洗牌过程的算法，通过给定的随机顺序和重复次数，实现了对一副包含54张牌的扑克牌进行洗牌。文章详细解释了洗牌过程，并提供了具体的实现代码。

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（来自PAT（Advance Level）Practice 1042）
题目
Shuffling is a procedure used to randomize a deck of playing cards. Because standard shuffling techniques are seen as weak, and in order to avoid “inside jobs” where employees collaborate with gamblers by performing inadequate shuffles, many casinos employ automatic shuffling machines. Your task is to simulate a shuffling machine.
The machine shuffles a deck of 54 cards according to a given random order and repeats for a given number of times. It is assumed that the initial status of a card deck is in the following order:

S1, S2, ..., S13, 
H1, H2, ..., H13, 
C1, C2, ..., C13, 
D1, D2, ..., D13, 
J1, J2

where “S” stands for “Spade”, “H” for “Heart”, “C” for “Club”, “D” for “Diamond”, and “J” for “Joker”. A given order is a permutation of distinct integers in [1, 54]. If the number at the i-th position is j, it means to move the card from position i to position j. For example, suppose we only have 5 cards: S3, H5, C1, D13 and J2. Given a shuffling order {4, 2, 5, 3, 1}, the result will be: J2, H5, D13, S3, C1. If we are to repeat the shuffling again, the result will be: C1, H5, S3, J2, D13.
Input Specification:
Each input file contains one test case. For each case, the first line contains a positive integer K (≤20) which is the number of repeat times. Then the next line contains the given order. All the numbers in a line are separated by a space.
Output Specification:
For each test case, print the shuffling results in one line. All the cards are separated by a space, and there must be no extra space at the end of the line.
Sample Input:

2
36 52 37 38 3 39 40 53 54 41 11 12 13 42 43 44 2 4 23 24 25 26 27 6 7 8 48 49 50 51 9 10 14 15 16 5 17 18 19 1 20 21 22 28 29 30 31 32 33 34 35 45 46 47

Sample Output:

S7 C11 C10 C12 S1 H7 H8 H9 D8 D9 S11 S12 S13 D10 D11 D12 S3 S4 S6 S10 H1 H2 C13 D2 D3 D4 H6 H3 D13 J1 J2 C1 C2 C3 C4 D1 S5 H5 H11 H12 C6 C7 C8 C9 S2 S8 S9 H10 D5 D6 D7 H4 H13 C5

题目大意

给了54张扑克牌，分别标号为1-54，初始按编号从小到大给定花色排序（S1-S13,H1-H13,C1-C13,D1-D13,J1-J2）。

然后根据输入的两行数据：第一行K代表执行操作的次数；第二行给出的是每个位置上的牌在一次操作后的位置。

例如题目中给的例子：S3, H5, C1, D13 ,J2.五张牌在 {4, 2, 5, 3, 1}的操作序列下执行一次的结果为：J2,H5,D13,S3,C1（将S3放在第4个，H5放在第2个，C1放在第5个,D13放在第3个,J2放在第1个）;执行两次后的结果为：C1,H5,S3,J2,D13，以此类推，求出执行K次后的结果。

解题思路

首先需要一个数组存放扑克牌初始序列——start[N+1](int 型，存放的1-54)
再用一个数组存放操作序列（就是输入的那一行数字）——next[N+1]
然后就是操作后的序列——end[N+1]
操作可以表示为：end[next[i]]=start[i] //把第i个位置上的牌的编号存在位置next[i]上
然后再把end数组里面的值赋值给start数组。如此循环K次，这样K次之后start数组里面存的就是要求的结果序列
然后就是关于怎么输出，因为题目要求输出的扑克牌号，而不是序号，start数组中放的是1-54中的数字，代表序列，然后我们要将这个数字对应的扑克牌求出来，输出。
数字X与扑克牌之间的转换关系，先求出花色：用一个char数组map存放五种花色，map[5]={'S','H','C','D','J'},如果当前牌号为X，则map[(X-1)/13]即为这张牌的花色，(X-1)%13+1，即为在对应花色下的编号。（关于之间的转换关系，可以在草稿纸上自己拿几个数字推导一下就出来了）

还要注意：一行的末尾不允许有空格！！！

代码如下

#include<bits/stdc++.h>
using namespace std;
const int N=54;
int main()
{
 int start[N+1],end[N+1],next[N+1],K;
 char map[5]={'S','H','C','D','J'};
 scanf("%d",&K);
 for(int i=1;i<=N;i++)
 {
  scanf("%d",&next[i]);
  start[i]=i;
 }
 for(int i=0;i<K;i++)
 {
  for(int j=1;j<=N;j++)
  {
   end[next[j]]=start[j];
  }
  for(int j=1;j<=N;j++)
  {
   start[j]=end[j];
  }
 }
 for(int i=1;i<=N;i++)
 {
  printf("%c%d",map[(start[i]-1)/13],(start[i]-1)%13+1);
     if(i<N)printf(" ");
 }
 return 0;
}