归并排序（Java）

    /**
     * 将数组合并
     *
     * @param nums
     * @param start 0
     * @param mid   4
     * @param end   7
     */
    private void merge(int[] nums, int start, int mid, int end) {
        int leftSize = mid - start;
        int rightSize = end - mid + 1;

        //左边的数组
        int[] leftNums = new int[leftSize];
        for (int i = start; i < mid; i++) {
            leftNums[i - start] = nums[i];
        }
        //右边的数组
        int[] rightNums = new int[rightSize];
        for (int i = mid; i <= end; i++) {
            rightNums[i - mid] = nums[i];
        }

        //排序并合并
        int left = 0;//左边数组的指针
        int right = 0;//右边数组的指针
        int index = start;
        while (left < leftSize && right < rightSize) {
            if (leftNums[left] < rightNums[right]) {//左边的小
                nums[index++] = leftNums[left++];
            } else {//右边小了
                nums[index++] = rightNums[right++];
            }
        }

        //剩余的也要赋值上去
        while (left < leftSize) {
            nums[index++] = leftNums[left++];
        }

        while (right < rightSize) {
            nums[index++] = rightNums[right++];
        }
    }

        int[] nums = new int[]{1, 3, 5, 9, 2, 4, 6, 8};
        merge(nums, 0, 4, nums.length - 1);
        for (int i : nums) {
            System.out.print(i + " ");
        }

    /**
     * 归并排序
     *
     * @param nums
     * @param start
     * @param end
     */
    public void uSort(int[] nums, int start, int end) {
        if (end == start) {//到达最小问题的条件，停止递归
            return;
        }

        int mid = (start + end) / 2;
        uSort(nums, start, mid);//排好 0 1
        uSort(nums, mid + 1, end);//排好 2 3
        merge(nums, start, mid + 1, end);//将0 1 2 3合并
    }

        int[] nums = new int[]{5, 7, 1, 3, 9, 0, 1};
        uSort(nums, 0, nums.length / 2, nums.length - 1);
        for (int i : nums) {
            System.out.print(i + " ");
        }