#include<iostream>#include<string>#include<vector>#include<stdio.h>#include <strings.h>using namespace std;enum { ALP = 26,};int key[ALP];int rev[ALP];void outKey(){ for (int i=0; i<ALP; ++i){ printf("%c", 'A'+key[i]); }}int getVal(char c){ if (isupper(c)){ return c-'A'; } return c-'a';}inline int toVal(char c){ return rev[getVal(c)];}char enc(char p, char c){ if (!isalpha(c)) return c; if (!isalpha(p)) p = 'a'; int t = toVal(c) - toVal(p); t = (t + ALP)%ALP; p = key[t] + 'a'; if (isupper(c)){ p = toupper(p); } return p;}char dec(char p, char c){ if (!isalpha(c)) return c; if (!isalpha(p)) p = 'a'; int t = toVal(c) + toVal(p); t = (t + ALP)%ALP; p = key[t] + 'a'; if (isupper(c)){ p = toupper(p); } return p;}int changeKey(char *str = NULL){ int i; if (str==0){ for (i=0; i<ALP; ++i){ key[i] = i; rev[i] = i; } return 0; } int j=0; bool vis[ALP] = {false}; for (i=0; str[i]; ++i){ if (!isalpha(str[i])) continue; int t = getVal(str[i]); if (vis[t]){ changeKey(NULL); return -1; } vis[t] = true; rev[t] = j; key[j++] = t; } if (j<ALP){ changeKey(NULL); return -1; } return 0;}char cmd[100];char line[10004];void encrypt(){ char p = 'a'; for (int i=0; line[i]; ++i){ char t = enc(p, line[i]); p = line[i]; line[i] = t; } printf("RESULT: %s", line);}void decrypt(){ char p = 'a'; for (int i=0; line[i]; ++i){ line[i] = dec(p, line[i]); p = line[i]; } printf("RESULT: %s", line);}void fun(){ while(scanf("%s", cmd) > 0){ fgets(line, 10004, stdin); if (strcasecmp(cmd, "ENCRYPT")==0){ encrypt(); } else if(strcasecmp(cmd, "DECRYPT")==0){ decrypt(); } else if(strcasecmp(cmd, "CIPHER")==0){ if (0==changeKey(line)){ printf("Good cipher. Using "); outKey(); printf(".n"); } else { printf("Bad cipher. Using default.n"); } } else { printf("Command not understood.n"); } }}int main(){ changeKey(0); fun(); return 0;}
