二分归并排序

二分归并的思想主要是分治思想,可以借助递归树来辅助思考如何分解合并

  • 分解 :将原问题分解成若干个子问题
  • 解决:递归地求解各个子问题,若子问题足够小,则直接求解;
  • 合并:将子问题的结果合并成原问题

package com.wuzhixin.test;

import java.util.Arrays;

public class BinarySort {

    public static void main(String[] args) {
        int arr[] = {11, 33, 22, 4, 5, 3, 99, 65};
        merge(arr, 0, arr.length -1);
        System.out.println(Arrays.toString(arr));


    }

    public static void merge(int arr[], int start, int end) {
        int middle = (start+end)/2;
        if(start<end){
            merge(arr,start,middle);
          //  System.out.println("******");
            merge(arr,middle+1,end);
         //   System.out.println("22222222");
            mergeSort(arr,start,middle,end);
            System.out.println("+++++++");
        }
    }


    public static void mergeSort(int arr[], int start,int middle, int end) {
        int mid = (start + end) / 2+1;
        int startIndex = start;
        int endIndex = end;
        int count = 0;
        int midIndex = middle;

        int []real = new int[end-start+1];
        while (startIndex <= midIndex && mid <= endIndex) {
            if (arr[startIndex] < arr[mid] && startIndex <= midIndex) {
                real[count++] = arr[startIndex++];

            }
            if (arr[startIndex] > arr[mid] && mid <=endIndex) {
                real[count++] = arr[mid++];

            }
        }

        //当退出循环可能左边剩余,也可能右边剩余
        //左边剩余
        while (startIndex <= midIndex) {
            real[count++] = arr[startIndex++];
        }

        //右边剩余
        while (mid <=end) {
            real[count++] = arr[mid++];
        }


        for (int i = 0; i < real.length; i++) {
            arr[i+start]=real[i];

        }
    }
}

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