merge sort algorithm in java code example

Example 1: merge sort java

public static void mergeSort(int[] a, int n) {
    if (n < 2) {
        return;
    }
    int mid = n / 2;
    int[] l = new int[mid];
    int[] r = new int[n - mid];
 
    for (int i = 0; i < mid; i++) {
        l[i] = a[i];
    }
    for (int i = mid; i < n; i++) {
        r[i - mid] = a[i];
    }
    mergeSort(l, mid);
    mergeSort(r, n - mid);
 
    merge(a, l, r, mid, n - mid);
}

public static void merge(
  int[] a, int[] l, int[] r, int left, int right) {
 
    int i = 0, j = 0, k = 0;
    while (i < left && j < right) {
        if (l[i] <= r[j]) {
            a[k++] = l[i++];
        }
        else {
            a[k++] = r[j++];
        }
    }
    while (i < left) {
        a[k++] = l[i++];
    }
    while (j < right) {
        a[k++] = r[j++];
    }
}

Example 2: Merge sort java

public class JavaMergeSort
{
   void sorting(int[] num, int left, int main, int right)
   {
      // finding size of two sub arrays
      int list1 = main - left + 1;
      int list2 = right - main;
      // creating temporary array
      int[] L = new int[list1];
      int[] R = new int[list2];
      // copying data to temporary array
      for(int a = 0; a < list1; ++a)
         L[a] = num[left + a];
      for(int b = 0; b < list2; ++b)
         R[b] = num[main + 1+ b];
      // existing index of first and second sub array
      int p = 0, q = 0;
      // existing index of merged sub array
      int r = left;
      while(p < list1 && q < list2)
      {
         if(L[p] <= R[q])
         {
            num[r] = L[p];
            p++;
         }
         else
         {
            num[r] = R[q];
            q++;
         }
         r++;
      }
      // copying remaining elements of L[] array
      while(p < list1)
      {
         num[r] = L[p];
         p++;
         r++;
      }
      // copying remaining elements of R[] array
      while(q < list2)
      {
         num[r] = R[q];
         q++;
         r++;
      }
   }
   // function that sorts
   void sort(int[] arrNum, int l, int r)
   {
      if(l < r)
      {
         // finding middle point
         int m = (l + r) / 2;
         // sorting first and second list
         sort(arrNum, l, m);
         sort(arrNum , m+1, r);
         // merging sorted list
         sorting(arrNum, l, m, r);
      }
   }
   // display array
   static void displayArray(int[] arr)
   {
      int number = arr.length;
      for(int a = 0; a < number; ++a)
         System.out.print(arr[a] + " ");
      System.out.println();
   }
   public static void main(String[] args)
   {
      int[] arrNumbers = {33, 00, 55, 11, 22, 44};
      System.out.println("Before sorting - ");
      displayArray(arrNumbers);
      JavaMergeSort obj = new JavaMergeSort();
      obj.sort(arrNumbers, 0, arrNumbers.length - 1);
      System.out.println("\nAfter sorting - ");
      displayArray(arrNumbers);
   }
}

Example 3: how to write a merge sort array method ni java

public static void merge(
  int[] a, int[] l, int[] r, int left, int right) {
  
    int i = 0, j = 0, k = 0;
    while (i < left && j < right) {
        if (l[i] <= r[j]) {
            a[k++] = l[i++];
        }
        else {
            a[k++] = r[j++];
        }
    }
    while (i < left) {
        a[k++] = l[i++];
    }
    while (j < right) {
        a[k++] = r[j++];
    }
}

Example 4: merge sort algorithm

/*  
    a[] is the array, p is starting index, that is 0, 
    and r is the last index of array. 
*/

#include <stdio.h>

// lets take a[5] = {32, 45, 67, 2, 7} as the array to be sorted.

// merge sort function
void mergeSort(int a[], int p, int r)
{
    int q;
    if(p < r)
    {
        q = (p + r) / 2;
        mergeSort(a, p, q);
        mergeSort(a, q+1, r);
        merge(a, p, q, r);
    }
}

// function to merge the subarrays
void merge(int a[], int p, int q, int r)
{
    int b[5];   //same size of a[]
    int i, j, k;
    k = 0;
    i = p;
    j = q + 1;
    while(i <= q && j <= r)
    {
        if(a[i] < a[j])
        {
            b[k++] = a[i++];    // same as b[k]=a[i]; k++; i++;
        }
        else
        {
            b[k++] = a[j++];
        }
    }
  
    while(i <= q)
    {
        b[k++] = a[i++];
    }
  
    while(j <= r)
    {
        b[k++] = a[j++];
    }
  
    for(i=r; i >= p; i--)
    {
        a[i] = b[--k];  // copying back the sorted list to a[]
    } 
}

// function to print the array
void printArray(int a[], int size)
{
    int i;
    for (i=0; i < size; i++)
    {
        printf("%d ", a[i]);
    }
    printf("\n");
}
 
int main()
{
    int arr[] = {32, 45, 67, 2, 7};
    int len = sizeof(arr)/sizeof(arr[0]);
 
    printf("Given array: \n");
    printArray(arr, len);
    
    // calling merge sort
    mergeSort(arr, 0, len - 1);
 
    printf("\nSorted array: \n");
    printArray(arr, len);
    return 0;
}