二分查找模版

二分：精确查找

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
int main()
{
    int target,i,j,mid,r,l;
    int a[]={1,1,2,2,3,5};
    cout<<a[5]<<endl;
    target=3;
    l=0;r=6;
    while(r>=l)
    {
        mid=(r+l)>>1;
        if(a[mid]==target)
        break;
        else if(a[mid]<target)
        l=mid+1;
        else
        r=mid-1;
    }
    printf("%d
",mid);
}

二分上限查找：

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
int main()
{
    int target,i,j,mid,r,l;
    int a[]={2,2,2,2,5,6};
    //cout<<a[5]<<endl;
    target=2;
    l=0;r=6;
    mid=(l+r)>>1;
    while(r>l)
    {
        if(a[mid]>target)
        r=mid;
        else
        l=mid+1;
        mid=(l+r)>>1;
    }
    printf("%d
",mid);
}

二分下限查找：

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
int main()
{
    int target,i,j,mid,r,l;
    int a[]={1,2,2,2,3,6};
    //cout<<a[5]<<endl;
    target=2;
    l=0;r=6;
    mid=(l+r+1)>>1;
    while(r>l)
    {
        if(a[mid]<target)
        l=mid;
        else
        r=mid-1;
        mid=(l+r+1)>>1;
    }
    printf("%d
",mid);
}