二分查找一个数

Posted 2020-10-09

#include <bits/stdc++.h>
using namespace std;
inline int read(){
    int num=0,f=1; char c=getchar();
    while(!isdigit(c)){if(c==‘-‘) f=-1; c=getchar();}
    while(isdigit(c)){num=(num<<1)+(num<<3)+(c^48); c=getchar();}
    return num*f;
}
int a[100],n,m;
inline int in(){
    n=read();
    for(int i=1;i<=n;i++) a[i]=read();
    m=read();
}
int lower_bound(int size,int key){ 
    int len=size,l=1,r=size,mid,dir;
    while(l<r){
        len>>=1;
        dir=l+len;
        if(a[dir]<key) l=dir+1;
        if(a[dir]>key) r=dir-1;
        if(a[dir]==key){
            l=dir; break;
        }
    }    
    return l;
}
inline int work(){
    cout<<lower_bound(n,m);
}
int main(){
    in();
    work();
}