MergeSort.java

import java.util.Arrays;

public class MergeSort {

    public static void main(String[] args) {

        // testing merge function
        int[] arr = { 1, 3, 4, -1, 0 };
        // merge(arr, 0, 2, 4);
        System.out.println(Arrays.toString(arr));

        // testing merge sort
        int[] arr2 = new int[] { 4, 6, -1, 7, 3, 0, 9 };
        mergeSort(arr2, 0, arr2.length - 1);
        System.out.println(Arrays.toString(arr2));

    }

    public static void mergeSort(int[] arr, int lo, int hi) {
        if (lo < hi) {
            int mid = lo + (hi - lo) / 2;
            mergeSort(arr, lo, mid);
            mergeSort(arr, mid + 1, hi);
            merge(arr, lo, mid, hi);
        }
    }



    public static void merge(int[] arr, int lo, int mid, int hi) {
        int[] temp = new int[hi - lo + 1];
        int i = lo;
        int j = mid + 1;
        int k = 0;
        while (i <= mid && j <= hi) {
            if (arr[i] <= arr[j]) {
                temp[k++] = arr[i++];
            } else {
                temp[k++] = arr[j++];
            }
        }
        while (i <= mid) {
            temp[k++] = arr[i++];
        }
        while (j <= hi) {
            temp[k++] = arr[j++];
        }
        for (int z = lo; z <= hi; z++) {
            arr[z] = temp[z-lo];
        }
    }
}