program to print in zig zag fashion

ZigZag.java

import java.util.Scanner;

public class ZigZag {

  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    String input = "I am Lord Voldemort. Lord Voldemort is my past, my present and my future!!!"; //sc.next();
    System.out.print("Enter value of K: ");
    int K = sc.nextInt();
    System.out.println();

    for (int i = 0; i < K; i++) {
      StringBuilder sb = new StringBuilder();
      sb.append(new String(new char[i]).replace('\0', ' ')); // logic may be changed to create string of spaces
      int index = i;
      boolean up = i == K - 1; // for all lines except last, we start by moving down
      while(index < input.length()) {
        sb.append(input.charAt(index)); // append char

        int gapSize; // compute and append spaces
        if (up) {
          gapSize = 2 * i - 1;
        } else {
          int j = K - i - 1;
          gapSize = 2 * j - 1;
        }
        sb.append(new String(new char[gapSize]).replace('\0', ' ')); // logic may be changed to create string of spaces

        index += gapSize + 1; // index of next char for current line
        // set direction for next character
        if (i == 0) { // for top line always consider we are moving down
          up = false;
        } else if (i == K - 1) { // for last line always consider we are moving up
          up = true;
        } else { // for middle lines we alaternatively move down and up
          up = !up;
        }
      }
      System.out.println(sb.toString());
    }
  }
}