数的范围

acwing789
STL

const int N=1e5+10;
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 st=lower_bound(a,a+n,x)-a;
        if(st == n || a[st] != x)
        {
            cout<<-1<<' '<<-1<<endl;
            continue;
        }
        int ed=upper_bound(a,a+n,x)-a;
        cout<<st<<' '<<ed-1<<endl;
    }

    //system("pause");
}

手写二分

const int N=1e5+10;
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;

        while(l<r)
        {
            int mid=l+r>>1;
            if(a[mid] >= x) r=mid;
            else l=mid+1;
        }

        if(r == n || a[r] != x)
        {
            cout<<-1<<' '<<-1<<endl;
            continue;
        }
        
        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;
    }

    //system("pause");
}