二分查找模版

二分：精确查找

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<algorithm>
 5 using namespace std;
 6 int main()
 7 {
 8     int target,i,j,mid,r,l;
 9     int a[]={1,1,2,2,3,5};
10     cout<<a[5]<<endl;
11     target=3;
12     l=0;r=6;
13     while(r>=l)
14     {
15         mid=(r+l)>>1;
16         if(a[mid]==target)
17         break;
18         else if(a[mid]<target)
19         l=mid+1;
20         else
21         r=mid-1;
22     }
23     printf("%d\n",mid);
24 }

二分上限查找：

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<algorithm>
 5 using namespace std;
 6 int main()
 7 {
 8     int target,i,j,mid,r,l;
 9     int a[]={2,2,2,2,5,6};
10     //cout<<a[5]<<endl;
11     target=2;
12     l=0;r=6;
13     mid=(l+r)>>1;
14     while(r>l)
15     {
16         if(a[mid]>target)
17         r=mid;
18         else
19         l=mid+1;
20         mid=(l+r)>>1;
21     }
22     printf("%d\n",mid);
23 }

二分下限查找：

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<algorithm>
 5 using namespace std;
 6 int main()
 7 {
 8     int target,i,j,mid,r,l;
 9     int a[]={1,2,2,2,3,6};
10     //cout<<a[5]<<endl;
11     target=2;
12     l=0;r=6;
13     mid=(l+r+1)>>1;
14     while(r>l)
15     {
16         if(a[mid]<target)
17         l=mid;
18         else
19         r=mid-1;
20         mid=(l+r+1)>>1;
21     }
22     printf("%d\n",mid);
23 }