排序算法图解之Java归并排序的实现

import java.util.Arrays;

/**
 * @author 兴趣使然黄小黄
 * @version 1.0
 * 递归实现归并排序
 */
@SuppressWarnings({"all"})
public class MergetSort {
    static int count = 0;

    public static void main(String[] args) {
        int[] arr = {8, 4, 5, 7, 1, 3, 6, 2};
        int[] temp = new int[arr.length];
        mergeSort(arr, 0, arr.length - 1, temp);
        System.out.println("归并排序后: arr[] = " + Arrays.toString(arr));
    }

    //归并排序
    public static void mergeSort(int[] arr, int left, int right, int[] temp){
        if (left < right){
            int mid = left - (left - right) / 2;
            //向左递归分解
            mergeSort(arr, left, mid, temp);
            //向右递归分解
            mergeSort(arr, mid + 1, right, temp);
            //排序 合并
            merge(arr, left, mid, right, temp);
        }
    }

    /**
     * 合并的方法
     * @param arr  排序的原始数组
     * @param left  左边有序序列的初始索引
     * @param mid  中间索引
     * @param right  右边索引
     * @param temp  中转数组
     */
    public static void merge(int[] arr, int left, int mid, int right, int[] temp){
        int i = left; //初始化i，左边有序序列的初始索引
        int j = mid + 1; //初始化j，右边有序序列的初始索引
        int t = 0; //指向temp数组的当前索引
        //先把左右两边有序数据按照规则填充到temp数组，直到左右两边有一边处理完毕
        while (i <= mid && j <= right){
            if (arr[i] <= arr[j]){
                temp[t] = arr[i];
                t++;
                i++;
            }else {
                temp[t] = arr[j];
                t++;
                j++;
            }
        }
        //把剩余的一方依次填充到temp数组
        while (i <= mid){ //左边序列还有剩余的元素
            temp[t++] = arr[i++];
        }
        while (j <= right){ //右边序列还有剩余的元素
            temp[t++] = arr[j++];
        }
        //将temp数组的元素拷贝到arr
        //拷贝每次小序列
        t = 0;
        int tempLeft = left;
        while (tempLeft <= right){
            arr[tempLeft++] = temp[t++];
        }
//        System.out.println("=====" + Arrays.toString(arr));
//        System.out.println(Arrays.toString(temp));
        count++;
        System.out.println("第" + count + "次合并: arr[] = " + Arrays.toString(arr));
//        System.out.println("第" + count + "次合并: temp[] = " + Arrays.toString(temp));
    }
}