二分模版

#include <iostream>
using namespace std;
const int N=100010;
int a[N];
int main()
{
    int n,m;cin>>n>>m;
    for(int i=0;i<n;i++) cin>>a[i];
    while(m--)
    {
        int x;cin>>x;
        int l=0,r=n-1;
        while(l<r)
        {
            int mid= l+r >>1;
            if(a[mid] >= x) r=mid;
            else l=mid+1;
        }
        if(a[l]!=x) cout<<"-1 -1"<<endl;
        else
        {
            cout<<l<<" ";
            l=0,r=n-1;
            while(l<r)
            {
                int mid= l+r+1 >>1;
                if(a[mid] <= x) l=mid;
                else r=mid-1;
            }
            cout<<l<<endl;
        }
    }
    return 0;
}