排序算法-归并排序算法

/**
 * 归并排序
 */

import java.util.Arrays;

public class SkillMergeSort {
    public static void main(String[] args) {
        int[] nums = {4, 7, 3, 1, 9, 8, 2, 0, 6, 5};
        MergeSort tool = new MergeSort();
        tool.mergeSort(nums, 0, nums.length - 1);
    }
}

class MergeSort {
    public void mergeSort(int[] nums, int left, int right) {
        int mid = left + (right - left) / 2;  //这样写的原因是left和right可能非常大，直接相加可能出现反转

        if (left >= right) {
            return;
        }

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

        sort(nums, left, mid, right);
        System.out.println(Arrays.toString(nums));
    }

    private void sort(int[] nums, int left, int mid, int right) {
        int[] temp = new int[nums.length];
        int i = left;
        int j = mid + 1;
        int index = 0;

        while (i <= mid && j <= right) {
            if (nums[i] < nums[j]) {
                temp[index] = nums[i];
                i++;
            } else {
                temp[index] = nums[j];
                j++;
            }
            index++;
        }

        while (i <= mid) {
            temp[index] = nums[i];
            i++;
            index++;
        }

        while (j <= right) {
            temp[index] = nums[j];
            j++;
            index++;
        }

        for (int k = 0; k < index; k++) {
            nums[left + k] = temp[k];
        }
    }
}

初始序列：
[4, 7, 3, 1, 9, 8, 2, 0, 6, 5]

运行结果：
[4, 7, 3, 1, 9, 8, 2, 0, 6, 5]
[3, 4, 7, 1, 9, 8, 2, 0, 6, 5]
[3, 4, 7, 1, 9, 8, 2, 0, 6, 5]
[1, 3, 4, 7, 9, 8, 2, 0, 6, 5]
[1, 3, 4, 7, 9, 2, 8, 0, 6, 5]
[1, 3, 4, 7, 9, 0, 2, 8, 6, 5]
[1, 3, 4, 7, 9, 0, 2, 8, 5, 6]
[1, 3, 4, 7, 9, 0, 2, 5, 6, 8]
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]