class RailFence {

// function to encrypt a message

public static String encryptRailFence(String text, int key)

{

// create the matrix to cipher plain text

// key = rows , length(text) = columns

char[][] rail = new char[key][text.length()];

// filling the rail matrix to distinguish filled

// spaces from blank ones

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++) {

// check the direction of flow

// reverse the direction if we've just

// filled the top or bottom rail

if (row == 0 || row == key - 1)

dirDown = !dirDown;

// fill the corresponding alphabet

rail[row][col++] = text.charAt(i);

// find the next row using direction flag

if (dirDown)

row++;

else

row--;

}

// now we can construct the cipher using the rail

// matrix

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();

}

// This function receives cipher-text and key

// and returns the original text after decryption

public static String decryptRailFence(String cipher, int key)

{

// create the matrix to cipher plain text

// key = rows , length(text) = columns

char[][] rail = new char[key][cipher.length()];

// filling the rail matrix to distinguish filled

// spaces from blank ones

for (int i = 0; i < key; i++)

Arrays.fill(rail[i], '\n');

// to find the direction

boolean dirDown = true;

int row = 0, col = 0;

// mark the places with '*'

for (int i = 0; i < cipher.length(); i++) {

// check the direction of flow

if (row == 0)

dirDown = true;

if (row == key - 1)

dirDown = false;

// place the marker

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

// find the next row using direction flag

if (dirDown)

row++;

else

row--;

}

// now we can construct the fill the rail matrix

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++) {

// check the direction of flow

if (row == 0)

dirDown = true;

if (row == key - 1)

dirDown = false;

if (rail[row][col] != '*')

result.append(rail[row][col++]);

// find the next row using direction flag

if (dirDown)

row++;

else

row--;

}

return result.toString();

}

public static void main(String[] args)

{

// Encryption

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));

// Now decryption of the same cipher-text

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));

}

}