DotheUntwist_1006

这个太简单了，没什么好说的

#include <stdio.h>#include <string.h>#define STRING_LEN_MAX 71char g_ciphertext[STRING_LEN_MAX];char g_plaintext[STRING_LEN_MAX];char g_Code2CharTable[] = {'_', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '.'};// c[i] = (p[ki % n] - i) % 28;//=>// ki % n = j => i = (j + xn)/k, //(j + xn)%k == 0//0<(j + xn)/k<n//=> //p[j] = c[(j + xn)/k] + 28*y + (j + xn)/k//0<c[(j + xn)/k] + 28*y + (j + xn)/k<28void TwistChar2Code(char* str, int iStringLen){for (int i = 0; i < iStringLen; i++){switch (str[i]){case '_':str[i] = 0;break;case 'a':str[i] = 1;break;case 'b':str[i] = 2;break;case 'c':str[i] = 3;break;case 'd':str[i] = 4;break;case 'e':str[i] = 5;break;case 'f':str[i] = 6;break;case 'g':str[i] = 7;break;case 'h':str[i] = 8;break;case 'i':str[i] = 9;break;case 'j':str[i] = 10;break;case 'k':str[i] = 11;break;case 'l':str[i] = 12;break;case 'm':str[i] = 13;break;case 'n':str[i] = 14;break;case 'o':str[i] = 15;break;case 'p':str[i] = 16;break;case 'q':str[i] = 17;break;case 'r':str[i] = 18;break;case 's':str[i] = 19;break;case 't':str[i] = 20;break;case 'u':str[i] = 21;break;case 'v':str[i] = 22;break;case 'w':str[i] = 23;break;case 'x':str[i] = 24;break;case 'y':str[i] = 25;break;case 'z':str[i] = 26;break;case '.':str[i] = 27;break;}}}void TwistCode2Char(char* str, int iStringLen){for (int i = 0; i < iStringLen; i++){str[i] = g_Code2CharTable[str[i]];}}void TwistingDecription(char* strCiphertext, int iStringLen, char* strPlaintext, int iKey){TwistChar2Code(strCiphertext, iStringLen);for (int i = 0; i < iStringLen; i++){// 遍历有效xint y = 0;int x = 0;for (x = (-i/iStringLen); x<(iKey-i/iStringLen); x++ ){if((i + x*iStringLen)%iKey != 0){continue;}// 寻找有效yy = (-g_ciphertext[(i+x*iStringLen)/iKey]-(i+x*iStringLen)/iKey)/28;break;}strPlaintext[i] = strCiphertext[(i + x*iStringLen)/iKey] + 28*y + (i + x*iStringLen)/iKey;}TwistCode2Char(strPlaintext, iStringLen);strPlaintext[iStringLen] = 0;}int main(){int iKey;while (scanf("%d %s", &iKey, g_ciphertext) != EOF && iKey != 0){TwistingDecription(g_ciphertext, strlen(g_ciphertext), g_plaintext, iKey);printf("%s\n", g_plaintext);}return 0;}