MergeSort.java

public class MergeSort {
    
    public static void mergeSort(int[] arr) {
        if (arr.length <= 1) {
            return;
        }
        
        // Split the array into two halves
        int mid = arr.length / 2;
        int[] left = new int[mid];
        int[] right = new int[arr.length - mid];
        
        // Copy elements to left and right arrays
        System.arraycopy(arr, 0, left, 0, mid);
        System.arraycopy(arr, mid, right, 0, arr.length - mid);
        
        // Recursively sort both halves
        mergeSort(left);
        mergeSort(right);
        
        // Merge the sorted halves
        merge(arr, left, right);
    }
    
    private static void merge(int[] arr, int[] left, int[] right) {
        int i = 0, j = 0, k = 0;
        
        // Merge left and right arrays in sorted order
        while (i < left.length && j < right.length) {
            if (left[i] <= right[j]) {
                arr[k++] = left[i++];
            } else {
                arr[k++] = right[j++];
            }
        }
        
        // Copy remaining elements from left array
        while (i < left.length) {
            arr[k++] = left[i++];
        }
        
        // Copy remaining elements from right array
        while (j < right.length) {
            arr[k++] = right[j++];
        }
    }
    
    public static void printArray(int[] arr) {
        for (int num : arr) {
            System.out.print(num + " ");
        }
        System.out.println();
    }
    
    public static void main(String[] args) {
        int[] numbers = {64, 34, 25, 12, 22, 11, 90};
        
        System.out.println("Original array:");
        printArray(numbers);
        
        mergeSort(numbers);
        
        System.out.println("Sorted array:");
        printArray(numbers);
    }
}