RSA

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 706    Accepted Submission(s): 524

Problem Description RSA is one of the most powerful methods to encrypt data. The RSA algorithm is described as follow:

> choose two large prime integer p, q

> calculate n = p × q, calculate F(n) = (p – 1) × (q – 1)

> choose an integer e(1 < e < F(n)), making gcd(e, F(n)) = 1, e will be the public key

> calculate d, making d × e mod F(n) = 1 mod F(n), and d will be the private key

You can encrypt data with this method :

C = E(m) = m
^e mod n

When you want to decrypt data, use this method :

M = D(c) = c
^d mod n

Here, c is an integer ASCII value of a letter of cryptograph and m is an integer ASCII value of a letter of plain text.

Now given p, q, e and some cryptograph, your task is to “translate” the cryptograph into plain text.  

Input Each case will begin with four integers p, q, e, l followed by a line of cryptograph. The integers p, q, e, l will be in the range of 32-bit integer. The cryptograph consists of l integers separated by blanks.  

Output For each case, output the plain text in a single line. You may assume that the correct result of plain text are visual ASCII letters, you should output them as visualable letters with no blank between them.  

Sample Input 101 103 7 11 7716 7746 7497 126 8486 4708 7746 623 7298 7357 3239  

Sample Output I-LOVE-ACM.  

Author JGShining（极光炫影）  

Source
杭电ACM省赛集训队选拔赛之热身赛  

Recommend Eddy       很可耻的， 枚举一下竟然AC了    

#include<stdio.h>
int main()
{
    int p,q,e,l;
    int c;
    int n;
    int fn;
    int temp;
    int d;
    while(scanf("%d%d%d%d",&p,&q,&e,&l)!=EOF)
    {
        n=p*q;
        fn=(p-1)*(q-1);
        d=1;
        while(d*e%fn!=1) d++;
        for(int i=0;i<l;i++)
        {
            scanf("%d",&c);
            temp=1;
            for(int j=0;j<d;j++)
            {
                temp=(temp*c)%n;
            }    
            printf("%c",temp);
        }    
        printf("\n");
    }    
    return 0;
}   

  太暴力了。其实应该用扩展欧几里德法去解方程的