题解 | 【模板】整数域二分

#include<bits/stdc++.h> 
#define ll long long
using namespace std;

ll a[200005];

void solve()
{
    ll n,q;
    cin>>n>>q;
    for(ll i=1;i<=n;i++)
    {
        cin>>a[i];
    }
    sort(a+1,a+n+1);
    while(q--)
    {
        ll l,r;
        cin>>l>>r;

        if(l>r)
        {
            cout<<0<<endl;
            continue;
        }

        ll ans;
        ll lpos=0,rpos=n+1,mid;
        while(lpos+1!=rpos)
        {
            mid=lpos+(rpos-lpos>>1);

            if(a[mid]<l)lpos=mid;
            else rpos=mid;
        }
        ans=rpos;  // 左起点下标

        rpos=n+1;
        while(lpos+1!=rpos)
        {
            mid=lpos+(rpos-lpos>>1);
            
            if(a[mid]<=r)lpos=mid;
            else rpos=mid;
        }
        ans=lpos-ans+1;
        cout<<ans<<endl;
    }

}

int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    solve();
    return 0;
}