java 简单搜索算法

Posted 2020-07-24 zhuzhuqwa

1 --无序查找
2     public static int Search(int[] a,int key){
3         for(int i=0;i<a.length;i++){
4             if(key==a[i]){
5                 return i;
6             }
7         }
8         return -1;
9     }

 1 --折半查找
 2     public static int BinarySearch(int[] a,int key){
 3         int min,max,mid;
 4         min=0;
 5         max=a.length-1;
 6         mid =(min+max)/2;
 7         while(key!=a[mid]){
 8             if(key>a[mid]){
 9                 min=mid+1;
10             }else{
11                 max=mid-1;
12             }
13             if(max<min)
14                 return -1;
15             
16             mid=(min+max)/2;
17         }
18         return mid;
19     }

 1 --折半查找优化
 2     public static int BinarySearch_2(int[] a,int key){
 3         int min,max,mid;
 4         min=0;
 5         max=a.length-1;    
 6         while(max>=min){
 7             mid =(min+max)>>1;
 8             if(key>a[mid]){
 9                 min=mid+1;
10             }else if(key<a[mid]){
11                 max=mid-1;
12             }else{
13                 return mid;
14             }
15         }
16         return -1;
17     }