MergeSort.java

import java.util.*;

public class MergeSort {
    public static void sort(Comparable[] arr) {
        Comparable[] temp = new Comparable[arr.length];
        sort(arr, temp, 0, arr.length - 1);
    }

    public static void sort(Comparable[] arr, Comparable[] aux, int lo, int hi) {
        if(lo >= hi) {
            return;
        }

        int mid = lo + (hi - lo) / 2;
        sort(arr, aux, lo, mid);
        sort(arr, aux, mid + 1, hi);
        merge(arr, aux, lo, mid, hi);
    }

    public static void merge(Comparable[] arr, Comparable[] aux, int lo, int mid, int hi) {
        for(int i = 0; i <= hi; i++) {
            aux[i] = arr[i];
        }

        int i = lo;
        int j = mid + 1;
        for(int k = lo; k <= hi; k++) {
            if(i > mid) {
                arr[k] = aux[j++];
            }
            else if(j > hi) {
                arr[k] = aux[i++];
            }
            else if(aux[i].compareTo(aux[j]) < 0) {
                arr[k] = aux[i++];
            }
            else {
                arr[k] = aux[j++];
            }
        }
        //System.out.println(Arrays.toString(arr));
    }

    public static void main(String[] args) {
        //Integer[] arr = {3, 27, 1, 42, 8, 7, 2, 5};
        Integer[] arr = {234,51,3,1,2,423,13,4};
        sort(arr);
        System.out.println(Arrays.toString(arr));
    }
}