POJ3087 Shuffle'm Up 模拟

Shuffle’m Up

Time Limit: 1000MS Memory Limit: 65536K
Total Submissions: 16500 Accepted: 7502
Description

A common pastime for poker players at a poker table is to shuffle stacks of chips. Shuffling chips is performed by starting with two stacks of poker chips, S1 and S2, each stack containing C chips. Each stack may contain chips of several different colors.

The actual shuffle operation is performed by interleaving a chip from S1 with a chip from S2 as shown below for C = 5:

The single resultant stack, S12, contains 2 * C chips. The bottommost chip of S12 is the bottommost chip from S2. On top of that chip, is the bottommost chip from S1. The interleaving process continues taking the 2nd chip from the bottom of S2 and placing that on S12, followed by the 2nd chip from the bottom of S1 and so on until the topmost chip from S1 is placed on top of S12.

After the shuffle operation, S12 is split into 2 new stacks by taking the bottommost C chips from S12 to form a new S1 and the topmost C chips from S12 to form a new S2. The shuffle operation may then be repeated to form a new S12.

For this problem, you will write a program to determine if a particular resultant stack S12 can be formed by shuffling two stacks some number of times.

Input

The first line of input contains a single integer N, (1 ≤ N ≤ 1000) which is the number of datasets that follow.

Each dataset consists of four lines of input. The first line of a dataset specifies an integer C, (1 ≤ C ≤ 100) which is the number of chips in each initial stack (S1 and S2). The second line of each dataset specifies the colors of each of the C chips in stack S1, starting with the bottommost chip. The third line of each dataset specifies the colors of each of the C chips in stack S2 starting with the bottommost chip. Colors are expressed as a single uppercase letter (A through H). There are no blanks or separators between the chip colors. The fourth line of each dataset contains 2 * C uppercase letters (A through H), representing the colors of the desired result of the shuffling of S1 and S2 zero or more times. The bottommost chip’s color is specified first.

Output

Output for each dataset consists of a single line that displays the dataset number (1 though N), a space, and an integer value which is the minimum number of shuffle operations required to get the desired resultant stack. If the desired result can not be reached using the input for the dataset, display the value negative 1 (−1) for the number of shuffle operations.

Sample Input
2
4
AHAH
HAHA
HHAAAAHH
3
CDE
CDE
EEDDCC
Sample Output

1 2
2 -1

问题连接

问题描述

起始有两堆都为c张牌组成的牌组s1,s2.
洗牌规则为:把s2和s1底部的牌交替的由下至上地放到另一个空地(s2先放)，最后s1的最顶部的牌也放到上面，组成新的牌s12.再取s12底部c张牌作为新的s1，剩下的c张牌为新的s2.
题意输入:
n为案例数。
然后每个案例都输入 c,代表两堆牌的牌数；字符串s1,s2,代表两牌组的起始位置；字符串s代表最终状态。
如果能够实现则输出:案例编号和最短洗牌次数。
如果不能实现则输出:案例编号和-1。

问题分析

模拟。洗牌动作使用string类能很好的实现。用set容器记录进行过的状态。
用BFS也可以，不过动作固定，产生的结果也是固定的，用队列好像就没什么必要了。

c++程序如下

#include<iostream>
#include<set>
#include<string>
using namespace std;
int c,steps;
string ss[3],s;
set<string>vis;
void shuffle();
int main()
{
	int n,t;
	bool flag;
	cin >> n;
	t = 0;
	while (n--)
	{
		cin >> c>>ss[1]>>ss[2]>>s;//ss[0]为题目中的s12
		t++;
		steps = 0;
		flag = 1;
		vis.clear();
		shuffle();
		vis.insert(ss[0]);
		while (s!=ss[0])
		{
			shuffle();
			if (vis.count(ss[0]))
			{
				flag = 0;
				break;
			}
			vis.insert(ss[0]);
		}
		if (flag) printf("%d %d\n", t, steps);
		else printf("%d -1\n", t);
	}
	return 0;
}
void shuffle()
{
	int i;
	ss[0] = "";
	for (i = 0; i < c; i++)
	{
		ss[0] += ss[2][i];
		ss[0] += ss[1][i];
	}
	ss[2] = ss[0].substr(c);
	ss[1] = ss[0].substr(0,c);
	steps++;
}