merge.java

import java.util.Arrays;

public class MergeSort {

    static void merge(int[] arr, int left, int mid, int right) {

        int n1 = mid - left + 1;
        int n2 = right - mid;

        int[] leftArr = new int[n1];
        int[] rightArr = new int[n2];

        for (int i = 0; i < n1; i++)
            leftArr[i] = arr[left + i];

        for (int j = 0; j < n2; j++)
            rightArr[j] = arr[mid + 1 + j];

        int i = 0, j = 0, k = left;

        while (i < n1 && j < n2) {
            if (leftArr[i] <= rightArr[j]) {
                arr[k] = leftArr[i];
                i++;
            } else {
                arr[k] = rightArr[j];
                j++;
            }
            k++;
        }

        while (i < n1) {
            arr[k] = leftArr[i];
            i++;
            k++;
        }

        while (j < n2) {
            arr[k] = rightArr[j];
            j++;
            k++;
        }
    }

    static void mergeSort(int[] arr, int left, int right) {

        if (left >= right)
            return;

        int mid = left + (right - left) / 2;

        mergeSort(arr, left, mid);
        mergeSort(arr, mid + 1, right);

        merge(arr, left, mid, right);
    }

    public static void main(String[] args) {

        int[] arr = {38, 27, 43, 3, 9, 82, 10};

        mergeSort(arr, 0, arr.length - 1);

        System.out.println("Sorted Array: " + Arrays.toString(arr));
    }
}