歸併排序實現（Java版）

歸併排序的時間複雜度（O(n log n)）要高於一般的排序算法，如冒泡等（O（n^2））；

具體實現如下：

public class MergeSort {
    public static void main(String[] args) {
        int[] array = {6, 1, 7, 9, 4, 3, 5};
        MergeSort sort = new MergeSort();
        int[] temp = new int[array.length];
        sort.mergeSort(array, 0, array.length - 1, temp);

        for (int i = 0; i < array.length; i++) {
            System.out.println(array[i]);
        }
    }

    private void mergeSort(int[] array, int start, int end, int[] temp) {
        int mid = start + (end - start) / 2;
        if (start >= end) return;
        mergeSort(array, start, mid, temp);
        mergeSort(array, mid + 1, end, temp);
        sort(array, start, mid, end, temp);
    }

    private void sort(int[] array, int start, int mid, int end, int[] temp) {
        int i = start;
        int j = mid + 1;
        int k = 0;
        while (i <= mid && j <= end) {
            if (array[i] > array[j]) {
                temp[k++] = array[j++];
            } else {
                temp[k++] = array[i++];
            }
        }

        while (i <= mid) {
            temp[k++] = array[i++];
        }

        while (j <= end) {
            temp[k++] = array[j++];
        }

        k = 0;
        while (start <= end) {
            array[start++] = temp[k++];
        }
    }
}