merge_sort.java

package datastructures;

public class merge_sort {

    // Main method to call mergeSort
    public static void main(String[] args) {
        int[] array = {12, 11, 13, 5, 6, 7};
        
        System.out.println("Given Array");
        printArray(array);
        
        merge_sort ob = new merge_sort();
        ob.mergeSort(array, 0, array.length - 1);
        
        System.out.println("\nSorted array");
        printArray(array);
    }

    // Method to sort an array using mergeSort
    public void mergeSort(int[] array, int left, int right) {
        if (left < right) {
            // Find the middle point
            int middle = left + (right - left) / 2;

            // Recursively sort the first and second halves
            mergeSort(array, left, middle);
            mergeSort(array, middle + 1, right);

            // Merge the sorted halves
            merge(array, left, middle, right);
        }
    }

    // Method to merge two subarrays
    public void merge(int[] array, int left, int middle, int right) {
        // Sizes of two subarrays to be merged
        int n1 = middle - left + 1;
        int n2 = right - middle;

        // Temporary 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] = array[left + i];
        for (int j = 0; j < n2; ++j)
            R[j] = array[middle + 1 + j];

        // Merge the temp arrays

        // Initial indexes of first and second subarrays
        int i = 0, j = 0;

        // Initial index of merged subarray array
        int k = left;
        while (i < n1 && j < n2) {
            if (L[i] <= R[j]) {
                array[k] = L[i];
                i++;
            } else {
                array[k] = R[j];
                j++;
            }
            k++;
        }

        // Copy remaining elements of L[] if any
        while (i < n1) {
            array[k] = L[i];
            i++;
            k++;
        }

        // Copy remaining elements of R[] if any
        while (j < n2) {
            array[k] = R[j];
            j++;
            k++;
        }
    }

    // Utility method to print the array
    public static void printArray(int[] array) {
        int n = array.length;
        for (int i = 0; i < n; ++i)
            System.out.print(array[i] + " ");
        System.out.println();
    }
}