RailFence.java

import java.util.Arrays;
class RailFence {
	public static String encryptRailFence(String text,int key)
	{
		char[][] rail = new char[key][text.length()];
		for (int i = 0; i < key; i++)
			Arrays.fill(rail[i], '\n');
		boolean dirDown = false;
		int row = 0, col = 0;
		for (int i = 0; i < text.length(); i++) {
			if (row == 0 || row == key - 1)
				dirDown = !dirDown;
			rail[row][col++] = text.charAt(i);
			if (dirDown)
				row++;
			else
				row--;
		}
		StringBuilder result = new StringBuilder();
		for (int i = 0; i < key; i++)
			for (int j = 0; j < text.length(); j++)
				if (rail[i][j] != '\n')
					result.append(rail[i][j]);
		return result.toString();
	}
	public static String decryptRailFence(String cipher,int key)
	{
		char[][] rail = new char[key][cipher.length()];
		for (int i = 0; i < key; i++)
			Arrays.fill(rail[i], '\n');
		boolean dirDown = true;
		int row = 0, col = 0;
		for (int i = 0; i < cipher.length(); i++) {
			if (row == 0)
				dirDown = true;
			if (row == key - 1)
				dirDown = false;

			rail[row][col++] = '*';

			if (dirDown)
				row++;
			else
				row--;
		}
		int index = 0;
		for (int i = 0; i < key; i++)
			for (int j = 0; j < cipher.length(); j++)
				if (rail[i][j] == '*'
					&& index < cipher.length())
					rail[i][j] = cipher.charAt(index++);
		StringBuilder result = new StringBuilder();
		row = 0;
		col = 0;
		for (int i = 0; i < cipher.length(); i++) {
			if (row == 0)
				dirDown = true;
			if (row == key - 1)
				dirDown = false;
			if (rail[row][col] != '*')
				result.append(rail[row][col++]);
			if (dirDown)
				row++;
			else
				row--;
		}
		return result.toString();
	}
	public static void main(String[] args)
	{
		System.out.println("Encrypted Message: ");
		System.out.println(
			encryptRailFence("attack at once", 2));
		System.out.println(
			encryptRailFence("GeeksforGeeks ", 3));
		System.out.println(
			encryptRailFence("defend the east wall", 3));
		System.out.println("\nDecrypted Message: ");
		System.out.println(
			decryptRailFence("atc toctaka ne", 2));
		System.out.println(
			decryptRailFence("GsGsekfrek eoe", 3));
		System.out.println(
			decryptRailFence("dnhaweedtees alf tl", 3));
	}
}