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:

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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 $K$ ( $\le 20$ ) 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:

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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:

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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

思路

实现随机洗牌。

核心就是一个不断的映射：

  • 位置1 = 打乱顺序（原始位置）
  • 位置2 = 打乱顺序（位置1）
  • 位置3 = 打乱顺序（位置2）
  • … …
  • 位置n = 打乱顺序（位置n-1）

我的实现里用了比较简化的代码，主要有两点：

  • 针对每张牌一次性进行多次位置变换，即
    • 最终位置 = 打乱（打乱（…打乱（原始位置）…））
  • 使用一点数学计算花色，而不是创建一个字符串数组。这点只是我有洁癖，代码的可读性有点损失
    • 打乱的时候变的是0到53的数字
    • 数字/13是花色，依次为SHCDJ
    • 数字%13是大小

代码

Github最新代码，欢迎交流

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#include <stdio.h>

int main()
{
	int count, order[54], deck[54], pos;
	char types[] = "SHCDJ";

	scanf("%d", &count);
	for (int i = 0; i < 54; i++)
		scanf("%d", order + i);

	for (int i = 0; i < 54; i++) {
		pos = i;
		for (int j = 0; j < count; j++)
			pos = order[pos] - 1;  /* the input order[] was 1 based */
		deck[pos] = i;
	}

	for (int i = 0; i < 54; i++) {
		printf("%c", types[deck[i] / 13]);
		printf("%d", deck[i] % 13 + 1);
		printf("%c", i == 53 ? '\0' : ' ');
	}

	return 0;
}