[leetcode]二分查找总结

 class Solution {
    public int[] searchRange(int[] A, int target) {
        int ans[]=new int[2];
      int a= bserch(A,target);
      if(a==-1) {ans[0]=-1;ans[1]=-1; return ans;}
     //left
     int b=a-1;
     while(b>=0&&A[b]==target) b--;
     ans[0]=b+1;
     b=a+1;
     
     while(b<=A.length-1&&A[b]==target) b++;
     ans[1]=b-1;
     return ans;
      
      
        
        
    }
    
    public  int bserch(int A[],int target)
    {
        int low=0;
        int end=A.length-1;
        while(low<=end)
        {
            int mid=(low+end)>>1;
            if(A[mid]==target) return mid;
            else if(A[mid]<target)  low=mid+1;
            else   end=mid-1;
            
        }
        
        return -1;
    }
   
        
        
   
    
    
}

 1  class Solution {
 2     public int[] searchRange(int[] A, int target) {
 3         int ans[]=new int[2];
 4       int a= bserch(A,target);
 5       if(a==-1) {ans[0]=-1;ans[1]=-1; return ans;}
 6      //left
 7      int b=a-1;
 8      while(b>=0&&A[b]==target) b--;
 9      ans[0]=b+1;
10      b=a+1;
11      
12      while(b<=A.length-1&&A[b]==target) b++;
13      ans[1]=b-1;
14      return ans;
15       
16       
17         
18         
19     }
20     
21     public  int bserch(int A[],int target)
22     {
23         int low=0;
24         int end=A.length-1;
25         while(low<=end)
26         {
27             int mid=(low+end)>>1;
28             if(A[mid]==target) return mid;
29             else if(A[mid]<target)  low=mid+1;
30             else   end=mid-1;
31             
32         }
33         
34         return -1;
35     }
36     public int  upperbound(int A[],int target) // the first one larger than target
37     {
38         int low=0;
39         int end=A.length-1;
40         while(low<=end)
41         {
42             int mid=(low+end)>>1;
43             if(A[mid]>target) end=mid-1;
44             else low=mid+1;
45             
46         }
47         return low;
48     }
49     public int  lowbound(int A[],int target) // the first one larger or equal  target
50     {
51         int low=0;
52         int end=A.length-1;
53         while(low<=end)
54         {
55             int mid=(low+end)>>1;
56             if(A[mid]>=target) end=mid-1;
57             else low=mid+1;
58             
59         }
60         return low;
61     }
62         
63         
64    
65     
66     
67 }