MergeSort.java

import java.util.Arrays;

public class MergeSort {
    public static void main(String[] args) {
        int[] arr={5,4,3,2,1};
        arr=mergeSort(arr);
        System.out.println(Arrays.toString(arr));
    }

static int[] mergeSort(int[] arr) {
    if (arr.length == 1) {
        return arr;
    }
    int mid = arr.length / 2;
    int[] left = mergeSort(Arrays.copyOfRange(arr, 0, mid));
    int[] right = mergeSort(Arrays.copyOfRange(arr, mid, arr.length));
    return merge(left, right);
}
private static int[] merge(int[] first,int[] second){
    int[] mix=new int[first.length+second.length];
    int i=0;
    int j=0;
    int k=0;
    while(i<first.length && j<second.length){
        if(first[i] < second[j]) {
            mix[k] = first[i];
            i++;
        }else{
            mix[k]=second[j];
            j++;
        }
        k++;
    }
    //it may be possible that one of the array is not complete
    while(i<first.length){
        mix[k]=first[i];
        i++;
        k++;
    }
    while(j<second.length){
        mix[k]=second[j];
        j++;
        k++;
    }
    return mix;
}
}