ZOJ Problem Set - 1009 Enigma

ZOJ Problem Set - 1009

Enigma

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Time Limit: 10 Seconds                                     Memory Limit: 32768 KB                            

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In World War II, Germany once used an electronic encryption machine called   Enigma, which played a decisive role in the initial victories of Nazi Germany.   It was proved to be one of the most reliable encryption systems in history.   However, it was the blind trust on the reliability of the machine that brought   about the doom of its user.

  The structure of a one-rotor Enigma is shown as follows (the Enigma has only   six keys):

The key element of the Enigma is the rotor, as shown in the second figure,   which uses electronic circuits to transform plaintext (input from keyboard)   into cryptograph (output on screen). When one key on the keyboard is pressed,   the corresponding cryptograph is shown on screen. Then the rotor will automatically   revolve a one-letter-step to a different position. The following figures illustrate   how the rotor works when letter "b" is pressed three successively   times:

When letter "b" is pressed for the first time, the signal goes through   the circuit and "A" is shown on screen. When the key is released,   the rotor revolves one-letter-step to a different position that changes all   the corresponding circuits so that each letter now has a different cryptograph.   When letter "b" is pressed for the second time, the corresponding   cryptograph is "C". So when letter "b" is pressed for the   third time, the cryptograph is "E" according to the principle specified   above.

  Now the following figure shows the structure of a two-rotor Enigma.

The difference is that when a key is released, the second rotor won't revolve   a step until the first one has finished one circle and returns to the original   position. This is also the same in the case of three-rotor Enigma. That is:   Only after the first rotor has finished one circle and return to the initial   status, the second rotor will revolve a step. And only after the second rotor   has finish one circle, the third rotor will revolve a step.

   However, how did the Allied Forces obtain the information encrypted by Enigma?   A person named Hans-Thilo Schimdt was very essential. He acted as a spy and   provided the initial status of the three rotors in each Enigma to the Allied   Forces once a month. The Allied Forces thus got everything they wanted by deciphering   the intercepted cryptograph using the information offered by the spy.

  Now, please design a program to obtain the plaintexts using the information   offered by the Allied Forces.

Input

  The input file contains several test cases representing several three-rotor   Enigmas. The last test case in the input file is followed by a line containing   a number 0.

  Each case begins with a line containing an integer m (1 <= m <= 26) which indicates   the number of sequential letters each rotor has. The first letter will always   be A. (for example, m = 6 tells each rotor has 6 keys from A to F). The following   three lines describe the initial status of the three rotors respectively. Each   of them contains a string consisting of m capital character. For instance, a   rotor with the initial status "BADFEC" indicates that the initial   encrypt mechanism is to convert "abcdef" to "BADFEC", that   is, original letter "a" corresponding to cryptograph letter "B",   "b" to "A", "c" to "D", "d"   to "F", "e" to "E" and "f" to "C".   The forth line of each case contains an integer n which tells the number of   cryptographs generated by the above Enigma. Then the following n lines are the   n cryptographs respectively, which consist of m capital characters each.

  Output

  For each test case, the output should consist of two parts. The first line is   the number of Enigma and a colon. The following lines are the plaintexts deciphered   from the corresponding cryptographs. Each plaintext should be printed in one   line. Note: The characters in the plaintext should be converted to the corresponding   lowercases before they are printed.

  Insert a blank line between test cases.

Sample Input

  6
  BADFEC
  ABCDEF
  ABCDEF
  1
  ACE
  0

Output for the Sample Input

  Enigma 1:
  bbb

 这题搞了我半天的时间，最后终于把思路给搞清楚了，首先是将初始值变成差值，规则如图：

滚动规则就是：第一个轮子：i%m 第二个轮子：(i/m)%m 第三个轮子：(i/(m*m))%m;原文到密文和密文到明文转动方向相反

#include<iostream>
#include<string>
#include<stdio.h>
using namespace std;
int main()
{
	int rotate[3];
	int rotor[3][30];
	int m;
	int cas=0;
	while(cin>>m&&m!=0)
	{
		cas++;
		if(cas!=1)cout<<endl;
		cout<<"Enigma "<<cas<<":"<<endl;
		for(int i=0;i<3;i++)
		{
			string str;
			cin>>str;
		    for(int j=0;j<m;j++)
		    {
		    	rotor[i][str[j]-'A']=str[j]-('A'+j);
                    }
		}
	    int n;
	    cin>>n;
	    for(int i=0;i<n;i++)
	    {
	    	string cytext;
	    	cin>>cytext;
			int len=cytext.length();
			for(int j=0;j<len;j++)
			{
			  rotate[0]=j%m;
			  rotate[1]=(j/m)%m;
			  rotate[2]=(j/(m*m))%m;
			  int index=cytext[j]-'A';
			  index=(index-rotor[2][(index-rotate[2]+m)%m]+m)%m;
			  index=(index-rotor[1][(index-rotate[1]+m)%m]+m)%m;
			  index=(index-rotor[0][(index-rotate[0]+m)%m]+m)%m;
			  cout<<(char)('a'+index);
			}
			cout<<endl;
	    }
	} 
}