數組總結

1冒泡排序和選擇排序

package hello;

import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.HashSet;
import java.util.Random;
import java.util.TreeSet;

public class Test02{
    public static void main(String[] args) throws Exception {
        //把數組拼接成一個字符串
        int[] arr={34,23,12,55,13};
        sort(arr);
        System.out.println(arrayToString2(arr));
        for(int x=0;x<arr.length-1;x++){
            for(int y=0;y<arr.length-1-x;y++){
                if(arr[y]>arr[y+1]){
                    int temp=arr[y];
                    arr[y]=arr[y+1];
                    arr[y+1]=temp;
                }
            }
        }
        System.out.println(arrayToString2(arr));
        
    }
    
    public static void sort(int[] arr){
        for(int x=0;x<arr.length-1;x++){
            for(int y=x+1;y<arr.length;y++){
                if(arr[y]<arr[x]){
                    int temp=arr[x];
                    arr[x]=arr[y];
                    arr[y]=temp;
                }
            }
        }
    }
    public static String arrayToString2(int[] arr){
        StringBuffer sb=new StringBuffer();
        sb.append("[");
        for(int i=0;i<arr.length;i++){
            if(i==arr.length-1){
                sb.append(arr[i]);
            }else{
                sb.append(arr[i]).append(", ");
                
            }
        }
        sb.append("]");
        return sb.toString();
    }
    public static String arrayToString(int[] arr){
        String s="";
        s+="[";
        for(int i=0;i<arr.length;i++){
            if(i==arr.length-1){
                s+=arr[i];
            }else{
                s+=arr[i];
                s+=", ";
            }
        }
        s+="]";
        return s;
    }
}

二分查找

package hello;

import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.HashSet;
import java.util.Random;
import java.util.TreeSet;

public class Test02{
    public static void main(String[] args) throws Exception {
        int[] arr={12,13,17,24,29,44};
        int mid=getIndex(arr, 14);
        System.out.println(mid);
        
    }
    public static int getIndex(int[] arr,int value){
        int max=arr.length-1;
        int min=0;
        
        int mid=(max+min)/2;
        
        while(arr[mid]!=value){
            if(arr[mid]>value){
                max=mid-1;
            }else if(arr[mid]<value){
                min=mid+1;
            }
            if(min>max){
                return -1;
            }
            mid=(max+min)/2;
        }
        return mid;
    }
}

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