Decrypting Mapping Cipher

本文介绍了一种基于字母映射表的密文解密算法实现。通过输入特定的字母映射密文及加密后的句子,算法能够准确地将密文还原为明文。示例展示了如何使用该算法进行解密操作。
题目: 先输入字母映射的密文, 再将输入的加密后的句子中的字母, 得其所对应密文中相同字母的位置, 将其位置的位数所对应字母表中的字母输出。(解密)

    Decrypting Mapping Cipher
Recall the Mapping Cipher laboratory work. You are given an alphabetic mapping
table to create cipher text. The table is defined by a string using 26 lower-case
alphabets, such as
incpfvztsmbexowhlgkqjyrdau
In the string all characters are different. Using this table to generate cipher text, it
performs the following mapping scheme:
a -> i, A->I
b -> n, B->N
c -> c, C->C
d -> p, D->P
. . . . . . .
y -> a, Y->A
z -> u, Z->U
Any non-alphabetic character are kept unchanged.
Apply the scheme to plain text:
There are 2 dogs and 3 cats.
It rains dogs & cats!
Obtain the following cipher text:
Qtfgf igf 2 pwzk iop 3 ciqk.
Sq gisok pwzk & ciqk!
Now, you are asked to do its inverse task. You are given the same mapping string, but
you will receive cipher text. Your mission is to decrypt the cipher text to a plain one.

Input
There are several test cases. Each test case starts with a line of mapping string used to
create cipher text. Following are cipher text enclosed by two lines of string "***".
Your task is to output the plain text before encryption. There is a blank line after each
case. Finally, you will reach a line of string "###" which signals the end of test.
Each line in test cases is no more than 1000 characters.

Output
The cipher text of each test case is prefixed with a plain text number as shown in the
sample output. Place a blank line between cases.

Sample Input
incpfvztsmbexowhlgkqjyrdau
***
Qtfgf igf 2 pwzk iop 3 ciqk.
Sq gisok pwzk & ciqk!
***
xowhlgkqjyrdauincpfvztsmbe
***
Vqlpl xpl 2 hikf xuh 3 wxvf.
Jv pxjuf hikf & wxvf!
***
###

Sample Output
Plain 1:
There are 2 dogs and 3 cats.
It rains dogs & cats!
Plain 2:
There are 2 dogs and 3 cats.
It rains dogs & cats!

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main()
{
	int flag=1, test=1;
	
	while(1)
	{
		char arr[26]={0}; //存取字母映射的密文
		char z[10]={0}; //存取密文后的***
		char str[1001]={0}; //存取输入的加密后的句子
		
		gets(arr);
		if(arr[0]=='#' && arr[1]=='#' && arr[2]=='#') break;
		
		gets(z);
		
		if(flag) flag=0;
		else printf("\n");
		
		printf("Plain %d:\n",test++);
		
		while(gets(str))
		{
			if(str[0]=='*' && str[1]=='*' && str[2]=='*') break;
			
			for(int i=0; i<strlen(str); i++)
			{
				if(str[i]>='a' && str[i]<='z' || str[i]>='A' && str[i]<='Z')
				{
					for(int j=0; j<26; j++)
					{
						if(str[i]==arr[j])
						{
							printf("%c",j+'a');
							break;
						}
						
						else if(str[i]+'a'-'A'==arr[j])
						{
							printf("%c",j+'A');
							break;
						}	
					}
				}
				
				else printf("%c",str[i]);
			}
			
			printf("\n");
		}
		
		scanf("\n");
			
	}
    
    return 0;
}



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