数组总结

1冒泡排序和选择排序

 1 package hello;
 2 
 3 import java.io.BufferedOutputStream;
 4 import java.io.File;
 5 import java.io.FileInputStream;
 6 import java.io.FileNotFoundException;
 7 import java.io.FileOutputStream;
 8 import java.io.IOException;
 9 import java.io.InputStreamReader;
10 import java.io.OutputStreamWriter;
11 import java.text.SimpleDateFormat;
12 import java.util.Date;
13 import java.util.HashSet;
14 import java.util.Random;
15 import java.util.TreeSet;
16 
17 public class Test02{
18     public static void main(String[] args) throws Exception {
19         //把数组拼接成一个字符串
20         int[] arr={34,23,12,55,13};
21         sort(arr);
22         System.out.println(arrayToString2(arr));
23         for(int x=0;x<arr.length-1;x++){
24             for(int y=0;y<arr.length-1-x;y++){
25                 if(arr[y]>arr[y+1]){
26                     int temp=arr[y];
27                     arr[y]=arr[y+1];
28                     arr[y+1]=temp;
29                 }
30             }
31         }
32         System.out.println(arrayToString2(arr));
33         
34     }
35     
36     public static void sort(int[] arr){
37         for(int x=0;x<arr.length-1;x++){
38             for(int y=x+1;y<arr.length;y++){
39                 if(arr[y]<arr[x]){
40                     int temp=arr[x];
41                     arr[x]=arr[y];
42                     arr[y]=temp;
43                 }
44             }
45         }
46     }
47     public static String arrayToString2(int[] arr){
48         StringBuffer sb=new StringBuffer();
49         sb.append("[");
50         for(int i=0;i<arr.length;i++){
51             if(i==arr.length-1){
52                 sb.append(arr[i]);
53             }else{
54                 sb.append(arr[i]).append(", ");
55                 
56             }
57         }
58         sb.append("]");
59         return sb.toString();
60     }
61     public static String arrayToString(int[] arr){
62         String s="";
63         s+="[";
64         for(int i=0;i<arr.length;i++){
65             if(i==arr.length-1){
66                 s+=arr[i];
67             }else{
68                 s+=arr[i];
69                 s+=", ";
70             }
71         }
72         s+="]";
73         return s;
74     }
75 }

二分查找

 1 package hello;
 2 
 3 import java.io.BufferedOutputStream;
 4 import java.io.File;
 5 import java.io.FileInputStream;
 6 import java.io.FileNotFoundException;
 7 import java.io.FileOutputStream;
 8 import java.io.IOException;
 9 import java.io.InputStreamReader;
10 import java.io.OutputStreamWriter;
11 import java.text.SimpleDateFormat;
12 import java.util.Date;
13 import java.util.HashSet;
14 import java.util.Random;
15 import java.util.TreeSet;
16 
17 public class Test02{
18     public static void main(String[] args) throws Exception {
19         int[] arr={12,13,17,24,29,44};
20         int mid=getIndex(arr, 14);
21         System.out.println(mid);
22         
23     }
24     public static int getIndex(int[] arr,int value){
25         int max=arr.length-1;
26         int min=0;
27         
28         int mid=(max+min)/2;
29         
30         while(arr[mid]!=value){
31             if(arr[mid]>value){
32                 max=mid-1;
33             }else if(arr[mid]<value){
34                 min=mid+1;
35             }
36             if(min>max){
37                 return -1;
38             }
39             mid=(max+min)/2;
40         }
41         return mid;
42     }
43 }