Merge Sort Java

PROGRAM TO IMPLEMENT MERGE SORT ALGORITHM

class MergeSort

{

    // Merges two subarrays of arr[].

    // First subarray is arr[l..m]

    // Second subarray is arr[m+1..r]

    void merge(int arr[], int l, int m, int r)

    {

        // Find sizes of two subarrays to be merged

        int n1 = m - l + 1;

        int n2 = r - m;

 

        /* Create temp arrays */

        int L[] = new int[n1];

        int R[] = new int[n2];

 

        /*Copy data to temp arrays*/

        for (int i = 0; i < n1; ++i)

            L[i] = arr[l + i];

        for (int j = 0; j < n2; ++j)

            R[j] = arr[m + 1 + j];

 

        /* Merge the temp arrays */

 

        // Initial indexes of first and second subarrays

        int i = 0, j = 0;

 

        // Initial index of merged subarry array

        int k = l;

        while (i < n1 && j < n2) {

            if (L[i] <= R[j]) {

                arr[k] = L[i];

                i++;

            }

            else {

                arr[k] = R[j];

                j++;

            }

            k++;

        }

 

        /* Copy remaining elements of L[] if any */

        while (i < n1) {

            arr[k] = L[i];

            i++;

            k++;

        }

 

        /* Copy remaining elements of R[] if any */

        while (j < n2) {

            arr[k] = R[j];

            j++;

            k++;

        }

    }

 

    // Main function that sorts arr[l..r] using

    // merge()

    void sort(int arr[], int l, int r)

    {

        if (l < r) {

            // Find the middle point

            int m = (l + r) / 2;

 

            // Sort first and second halves

            sort(arr, l, m);

            sort(arr, m + 1, r);

 

            // Merge the sorted halves

            merge(arr, l, m, r);

        }

    }

 

    /* A utility function to print array of size n */

    static void printArray(int arr[])

    {

        int n = arr.length;

        for (int i = 0; i < n; ++i)

            System.out.print(arr[i] + " ");

        System.out.println();

    }

 

    // Driver code

    public static void main(String args[])

    {

        int arr[] = { 12, 11, 13, 5, 6, 7 };

 

        System.out.println("Given Array");

        printArray(arr);

 

        MergeSort ob = new MergeSort();

        ob.sort(arr, 0, arr.length - 1);

 

        System.out.println("\nSorted array");

        printArray(arr);

    }

}







OUTPUT

Given array is 
12 11 13 5 6 7 
Sorted array is 
5 6 7 11 12 13 

CREDITS: https://www.geeksforgeeks.org/merge-sort/