用集合实现二分（折半）查找

 1 package com.cn.two;
 2 
 3 import java.util.ArrayList;
 4 import java.util.Collections;
 5 import java.util.List;
 6 import java.util.Scanner;
 7 
 8 public class Two {
 9   
10   //二分法
11   public static int find(List<Integer>list,int num){
12       int start = 0;
13       int end = list.size()-1;
14       while (start <= end){
15          int middle = (start + end)/2;
16          if (list.get(middle) == num){
17              return middle;
18          }else if(list.get(middle) < num){
19              start = middle + 1;
20          }else{
21              end = middle - 1;
22          }
23       }
24       return -1;
25   }
26   
27   public static void main(String[] args){
28       List<Integer> list =new ArrayList<Integer>();
29       Scanner input = new Scanner(System.in);
30       System.out.println("请输入需要查找的一组数字");
31       String str = input.nextLine();
32       String[] c = str.split(" ");
33       for(int i = 0 ;i < c.length;i++){
34           list.add(Integer.valueOf(c[i]));//把字符串数组的内容转成Integer并放入集合
35       }
36       Collections.sort(list);
37       System.out.println(list);
38       System.out.println("请输入需要查找的目标数字");
39       int num = input.nextInt();
40       int b = find(list,num);
41       if (b == -1){
42           System.out.println("没有" + num + "这个数");
43       }else {
44           System.out.println("找到" + num + "这个数，在" + b + "位置");
45       }
46   }
47 }