Google Count Pair

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

#pragma GCC target ("avx2")
#pragma GCC optimization ("O3")
#pragma GCC optimization ("unroll-loops")
#define ll  long long

// typedef tree<ll, null_type, less_equal<ll>, rb_tree_tag, tree_order_statistics_node_update> pbds;
// find_by_order, order_of_key

void solve(vector<ll> a, vector<ll> b, ll c, ll d);

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);

    ll t;
    t=1;
    // cin>>t;
    while(t--){
        solve({4,2,3,11, 6}, {1,2,2, 5, 4}, 1, 2);
    }

    return 0;
}

void solve(vector<ll> a, vector<ll> b, ll c, ll d){
    ll n = a.size();
    ll dcd = d-c;

    vector<ll> diff(n), diffS(n);

    for(ll i=0; i<n; ++i){
        diff[i] = a[i]-b[i];
        diffS[i] = diff[i];
    }

    sort(diffS.begin(), diffS.end());

    ll ct=0;

    for(int i=0; i<n-1; ++i){
        ll num = diff[i];

        ll pos = lower_bound(diffS.begin(), diffS.end(), num) - diffS.begin();

        diffS.erase(diffS.begin() + pos);

        ll k = upper_bound(diffS.begin(), diffS.end(), num-dcd) - diffS.begin();

        ll a = diffS.size()-k;

        ct += a;

    }

    cout<<ct<<endl;
}