冒泡排序,快排,二分查找

/**
 *冒泡
 * @author gx
 * @time 2022/1/21 10:47
 * 把每个元素依次和后面的每个元素进行比较
 */
public class BubbleSort {
    public static void main(String[] args) {
        int[] data = {2,3,4,523,23,433,21,213,43,432};

        System.out.println("冒泡前:\n"+ java.util.Arrays.toString(data));
        bubbleSort(data);
        System.out.println("冒泡后:\n"+ java.util.Arrays.toString(data));
    }
    private static void bubbleSort(int[] data) {
        int length = data.length;
        for (int i = 1; i < length; i++) {
            for (int j = 0; j < length - 1; j++) {
                if (data[j]>data[j+1]){//相邻元素对比,元素换位置
                    int temp = data[j+1];
                    data[j+1] = data[j];
                    data[j] = temp;
                }
            }
        }
    }
}

/**
 * @author gx
 * @time 2022/1/21 11:10
 * 快排总结:1.找一个基准点temp
 *          2.分别用i,j从数组左,右获取元素,与temp比较
 *          3.当i>temp,j<temp的时候进行交换元素
 *          4.遍历完后temp左边都是比他小的,右边都是大于的
 *          5.再递归左右
 */
public class QuickSort {
    public static void main(String[] args) {
        int[] data = {23,43,234,3,24,32,432,87,8753,32};
        System.out.println("排序之前：\n" + java.util.Arrays.toString(data));
        quickSort(data, 0, data.length - 1);
        System.out.println("排序之后：\n" + java.util.Arrays.toString(data));

    }

    private static void quickSort(int[] data, int low, int high) {
        int i,j,temp,t;
        if (low>high){
            return;
        }
        i = low;
        j = high;
        temp = data[low];
        while (i< j ){
            while (temp<=data[j]&&i<j){
                j--;
            }
            while (temp >=data[i]&&i<j){
                i++;
            }
            if (i<j){
                t=data[j];
                data[j] =data[i];
                data[i] =t;
            }
        }
        data[low] = data[i];
        data[i]=temp;
        quickSort(data,low,j-1);
        quickSort(data,j+1,high);
    }
}

package com.atguigu.jxc;

import java.util.ArrayList;
import java.util.List;

/**
 * @author gx
 * @time 2022/1/21 12:09
 */
public class BinarySearch {

       public static void main(String[] args){
           //注意：需要对已排序的数组进行二分查找
           int[] data = {1, 8, 10, 89, 1000, 1000,1000, 1234};
           List<Integer> list = binarySearch(data, 0, data.length, 1000);
           System.out.println(list);
       }

   private static List<Integer> binarySearch(int[] data, int left, int right, int find) {
      //先创建一个集合放找到的索引
      ArrayList<Integer> list = new ArrayList<>();
      if (left>right){//退出条件
         return list;
      }
      int mid = (left+right)/2;
      int midVal = data[mid];
      if (find < midVal){//向左
         return binarySearch(data,left,mid-1,find);
      }else if (find > midVal){//向右
         return binarySearch(data,mid+1,right,find);
      }else {//相等,如果下标是5,那么可能有相同的,左右各来一位,4,6,每次都看一下
         int temp= mid-1;
         while (true){
            if (temp <0 || data[temp] != find){
               break;
            }
            if (data[temp] == find){
               list.add(temp);
            }
            temp = temp-1;
         }
         list.add(mid);
         temp = mid+1;
         while (true){
            if (temp>data.length-1 || data[temp] != find){
               break;
            }
            if (data[temp] == find){
               list.add(temp);
            }
            temp = temp+1;
         }
         return list;
      }
   }
}