Java Program to sort elements using Merge Sort Technique

This a Java program which sorts all the elements using Merge Sort Technique. Merge sort is a divide and conquer technique , here the element list is divided into half and that halves are again divided into halves until only 2 elements left . Then compare those 2 elements , smallest one is kept first, repeat the same process until are the halves are sorted , and repeat the same process but in reverse order to unite the element list into one again.

See the animation below to understand ,

"Merge-sort-example" by Swfung8 - Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons.

PROGRAM :

package codingcorner.in;

import java.util.Scanner;

public class MergeSort {
 public static void main(String[] args) {
  int list[] = new int[50];
  int i, n;
  Scanner scan = new Scanner(System.in);
  System.out.print("How many numbers ? \t");
  n = scan.nextInt();
  System.out.print("\n\n");
  for (i = 0; i < n; i++) {
   System.out.print("Enter number " + (i + 1));
   list[i] = scan.nextInt();
  }
  scan.close();
  partition(list, 0, n - 1);
  System.out.print("\n\nAfter merge sort:\n");
  for (i = 0; i < n; i++) {
   System.out.print("\t" + list[i]);
  }
  System.out.print("\n\n");
 }

 private static void partition(int[] list, int low, int high) {
  int mid;

  if (low < high) {
   mid = (low + high) / 2;
   partition(list, low, mid);
   partition(list, mid + 1, high);
   mergeSort(list, low, mid, high);
  }

 }

 private static void mergeSort(int[] list, int low, int mid, int high) {
  int i, midd, k, loww;
  int[] temp = new int[50];
  loww = low;
  i = low;
  midd = mid + 1;
  while ((loww <= mid) && (midd <= high)) {
   if (list[loww] <= list[midd]) {
    temp[i] = list[loww];
    loww++;
   } else {
    temp[i] = list[midd];
    midd++;
   }
   i++;
  }
  if (loww > mid) {
   for (k = midd; k <= high; k++) {
    temp[i] = list[k];
    i++;
   }
  } else {
   for (k = loww; k <= mid; k++) {
    temp[i] = list[k];
    i++;
   }
  }

  for (k = low; k <= high; k++) {
   list[k] = temp[k];
  }

 }
}

OUTPUT :