Reverse Rot

Original Description

Idea

Use the symmetry of the structure: the first two pages are bundled with the last two and so on.

Given an odd P, the other three pages are P + 1, N - P and N - P + 1. For an even P, the other three pages are P - 1, N - P + 1 and N - P + 2.

Code

import java.util.*;
public class Reverse_Rot {

	public static void encrypt(String s, int k){
		for(int i = s.length()-1; i>=0; i--){
			char c = s.charAt(i);
			if(c == 95) c = 91;
			if(c == 46) c = 92;
			c = (char)(c + k);
			c = (char)((c - 'A') % 28 + 'A');
			if(c == 91) c = 95;
			if(c == 92) c = 46;
			System.out.print(c);
		}
		System.out.println();
	}
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner scan = new Scanner(System.in);
		while(scan.hasNext()){
			int k = scan.nextInt();
			if(k == 0)
				break;
			String s = scan.next();
			encrypt(s,k);
		}

	}

}