数的范围——二分

789. 数的范围 - AcWing题库

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