Merge Sort Algorithm | Java Programs

Output:

*** Merge Sort ***

--- Array Before ---
45, 23, 11, 89, 77, 9, 

--- Array After ---
9, 11, 23, 45, 77, 89,

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Solution:

/**
 *
 * source code by:
 * http://www.java2novice.com
 */
public class MergeSort {

    private int[] array;
    private int[] tempMergArr;
    private int length;

    public static void main(String a[]) {

        int[] inputArr = {45, 23, 11, 89, 77, 9};
        System.out.println("*** Merge Sort ***" + "\n");
        System.out.println("--- Array Before ---");
        for (int i : inputArr) {
            System.out.print(i + ", ");
        }
        MergeSort mms = new MergeSort();
        mms.sort(inputArr);
        System.out.println("\n");
        System.out.println("--- Array After ---");

        for (int i : inputArr) {
            System.out.print(i);
            System.out.print(", ");
        }
    }

    public void sort(int inputArr[]) {
        this.array = inputArr;
        this.length = inputArr.length;
        this.tempMergArr = new int[length];
        doMergeSort(0, length - 1);
    }

    private void doMergeSort(int lowerIndex, int higherIndex) {

        if (lowerIndex < higherIndex) {
            int middle = lowerIndex + (higherIndex - lowerIndex) / 2;
            // Below step sorts the left side of the array
            doMergeSort(lowerIndex, middle);
            // Below step sorts the right side of the array
            doMergeSort(middle + 1, higherIndex);
            // Now merge both sides
            mergeParts(lowerIndex, middle, higherIndex);
        }
    }

    private void mergeParts(int lowerIndex, int middle, int higherIndex) {

        for (int i = lowerIndex; i <= higherIndex; i++) {
            tempMergArr[i] = array[i];
        }
        int i = lowerIndex;
        int j = middle + 1;
        int k = lowerIndex;
        while (i <= middle && j <= higherIndex) {
            if (tempMergArr[i] <= tempMergArr[j]) {
                array[k] = tempMergArr[i];
                i++;
            } else {
                array[k] = tempMergArr[j];
                j++;
            }
            k++;
        }
        while (i <= middle) {
            array[k] = tempMergArr[i];
            k++;
            i++;
        }
    }
}