merge_sort.java

public class MergeSort {
    public static void mergeSort(int[] arr) {
        if (arr.length <= 1) {
            return; // Already sorted
        }

        // Split the array into two halves
        int middle = arr.length / 2;
        int[] left = new int[middle];
        int[] right = new int[arr.length - middle];

        System.arraycopy(arr, 0, left, 0, middle);
        System.arraycopy(arr, middle, right, 0, arr.length - middle);

        // Recursively sort both halves
        mergeSort(left);
        mergeSort(right);

        // Merge the sorted halves
        merge(arr, left, right);
    }

    public static void merge(int[] arr, int[] left, int[] right) {
        int i = 0, j = 0, k = 0;

        while (i < left.length && j < right.length) {
            if (left[i] <= right[j]) {
                arr[k++] = left[i++];
            } else {
                arr[k++] = right[j++];
            }
        }

        while (i < left.length) {
            arr[k++] = left[i++];
        }

        while (j < right.length) {
            arr[k++] = right[j++];
        }
    }

    public static void main(String[] args) {
        int[] arr = {12, 11, 13, 5, 6, 7};
        
        System.out.println("Original Array:");
        for (int value : arr) {
            System.out.print(value + " ");
        }
        
        mergeSort(arr);

        System.out.println("\nSorted Array:");
        for (int value : arr) {
            System.out.print(value + " ");
        }
    }
}