Cipher

Description

Bob and Alice started to use a brand-new encoding scheme. Surprisingly it is not a Public Key Cryptosystem, but their encoding and decoding is based on secret keys. They chose the secret key at their last meeting in Philadelphia on February 16th, 1996. They chose as a secret key a sequence of n distinct integers, a1 ; . . .; an, greater than zero and less or equal to n. The encoding is based on the following principle. The message is written down below the key, so that characters in the message and numbers in the key are correspondingly aligned. Character in the message at the position i is written in the encoded message at the position ai, where ai is the corresponding number in the key. And then the encoded message is encoded in the same way. This process is repeated k times. After kth encoding they exchange their message.

The length of the message is always less or equal than n. If the
message is shorter than n, then spaces are added to the end of the
message to get the message with the length n.

Help Alice and Bob and write program which reads the key and then a
sequence of pairs consisting of k and message to be encoded k times and
produces a list of encoded messages.

Input

The
input file consists of several blocks. Each block has a number 0 < n
<= 200 in the first line. The next line contains a sequence of n
numbers pairwise distinct and each greater than zero and less or equal
than n. Next lines contain integer number k and one message of ascii
characters separated by one space. The lines are ended with eol, this
eol does not belong to the message. The block ends with the separate
line with the number 0. After the last block there is in separate line
the number 0.

Output

Output
is divided into blocks corresponding to the input blocks. Each block
contains the encoded input messages in the same order as in input file.
Each encoded message in the output file has the lenght n. After each
block there is one empty line.

Sample Input

10
4 5 3 7 2 8 1 6 10 9
1 Hello Bob
1995 CERC
0
0

Sample Output

BolHeol  b
C RCE

题意 ： Bob和Alice想用一种新的加密方式，他们编码和译码都是依靠秘密钥匙，秘密钥匙选用一串数字a1,……an（0<ai<=n），编码要求：将信息(长度不大于n，如果小于n请自己补上空格)中i位置上的字符放到ai位置上
。这个过程经过K遍之后就成了加密后的信息。现在要求你写一个程序帮他们实现编码。

思路：　因为K会很大，　暴力会超时，　将其看作一个置换群，　求出每个循环的长度，　可知一个循环的长度即他的周期；　考虑求出每个循环的长度Ｌ，　对Ｋ取模，　然后再暴力求解；

#include <iostream>
#include <stdio.h>
#include <algorithm>
#include <string.h>
using namespace std;
const int maxn= ;

int main()
{
    int n;
    while(scanf("%d", &n) && n)
    {
        int hay[maxn], pos[maxn];
        for(int i =  ;i < n; i++)
        {
            scanf("%d",&hay[i]);
            hay[i] -= ;
        }
        for(int i =;i < n;i++)
        {
            pos[i] = ;
            int tmp = hay[i];
            while(tmp!=i)
            {
                pos[i]++;
                tmp = hay[tmp];
            }
        }
        int k;
        char s1[maxn], s2[maxn];
        while(scanf("%d", &k) && k)
        {
            getchar();
            gets(s1);
            if(strlen(s1) < n)
            {
                for(int i = strlen(s1); i<n; i++)
                    s1[i] = ' ';
                s1[n] = '\0';
            }
            for(int i = ; i < n; i++)
            {
                int tim = k%pos[i];
                int t = i;
                while(tim--)
                {
                    t = hay[t];
                }
                s2[t] = s1[i];
            }
            s2[n] = '\0';
            puts(s2);
        }
        printf("\n");
    }
    return ;

}