Decode

Time limit: 2000 ms

Memory limit: 65536 KB

 

Description

Julius Caesar used a system of cryptography, now known as Caesar Cipher, which shifted each letter 2 places further through the alphabet (e.g. ‘A’ shifts to ‘C’, ‘R’ shifts to ‘T’, etc.). At the end of the alphabet we wrap around, that is ‘Y’ shifts to ‘A’.

We can, of course, try shifting by any number. Given an encoded text and a number of places to shift, decode it.

For example, “TOPCODER” shifted by 2 places will be encoded as “VQREQFGT”. In other words, if given (quotes for clarity) “VQREQFGT” and 2 as input, you will return “TOPCODER”. See example 1 below.

Input Format

First line will be the cipher text String, between 0 to 50 characters (inclusive) long. Each character is an uppercase letter ‘A’ – ‘Z’.

Second line will be an integer shift (0 <= shift <= 25), which is the number of places to shift.

Output Format

The decoded String.

Sample Input 1

VQREQFGT
2

Sample Output 1

TOPCODER

Sample Input 2

ABCDEFGHIJKLMNOPQRSTUVWXYZ
10

Sample Output 2

QRSTUVWXYZABCDEFGHIJKLMNOP

Sample Input 3

TOPCODER
0

Sample Output 3

TOPCODER

Sample Input 4

ZWBGLZ
25

Sample Output 4

AXCHMA

Sample Input 5

DBNPCBQ
1

Sample Output 5

CAMOBAP

Sample Input 6

LIPPSASVPH
4

Sample Output 6

HELLOWORLD

 

Solution

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

int main()
{
    char str[50], alphabet[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    char * pch;
    int shift = 0, i, tempIndex;
    unsigned int size;
    fflush(stdin);
    scanf("%s",&str);
    scanf("%d",&shift);
    if(shift>=0 && shift <= 25){
        size = strlen(str);
        char result[size];
       // printf("%d %d",(pch-alphabet), strlen(str));
        for(i = 0 ; i < size; i++){
            pch =strchr(alphabet,str[i]);
            tempIndex = pch-alphabet;
            tempIndex = tempIndex - shift;
            if(tempIndex < 0){
                tempIndex = (unsigned)strlen(alphabet) + tempIndex;
            }
            result[i] =alphabet[tempIndex];
            printf("%c",result[i]);
        }
        printf("\n");
    }
    return 0;
}
Programming Problem Set #Decode Caesar Cipher

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