poj1317

简单模拟

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#include <iostream>

#include <cstdio>

#include <cstdlib>

#include <cstring>

using namespace std;



#define maxl 75



int key;

char cipher_text[maxl];

char plain_text[maxl];



bool is_letter(char ch)

{

    return ch <= 'z' && ch >= 'a';

}



int get_code(char ch)

{

    if (is_letter(ch))

        return ch - 'a' + 1;

    if (ch == '_')

        return 0;

    if (ch == '.')

        return 27;

    return -1;

}



char get_text(int a)

{

    if (a <= 26 && a >= 1)

        return a + 'a' - 1;

    if (a == 0)

        return '_';

    if (a == 27)

        return '.';

    return -1;

}



int unify(int a, int w)

{

    return (a % w + w) % w;

}



int main()

{

    //freopen("t.txt", "r", stdin);

    while (scanf("%d", &key), key)

    {

        scanf("%s", cipher_text);

        int len = strlen(cipher_text);

        for (int i = 0; i < len; i++)

            plain_text[unify(key * i, len)] = get_text(unify(get_code(cipher_text[i]) + i, 28));

        plain_text[len] = 0;

        puts(plain_text);

    }

    return 0;

}