Closest points

#include <bits/stdc++.h>

using namespace std;

long long distance(pair<long long, long long> p1, pair<long long, long long> p2) {
    return (p1.first - p2.first)*(p1.first - p2.first) + (p1.second - p2.second)*(p1.second - p2.second);
}

bool compare_y(pair<long long, long long> a, pair<long long, long long> b) {
    return a.second <= b.second;
}

int main() {

    int n;
    cin >> n;

    vector<pair<long long, long long>> points(n);
    for (int i = 0; i < n; i++)
        cin >> points[i].first >> points[i].second;

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

    long long d = distance(points[0], points[1]);

    for (int i = 1; i < n; i++) {

        int j = i-1;
        vector<pair<long long, long long>> around;

        while (j >= 0
            && abs(points[j].first - points[i].first)*abs(points[j].first - points[i].first) <= d) {
            around.push_back(points[j]);
            j -= 1;
        }

        sort(around.begin(), around.end(), compare_y);

        int size = (int) around.size();

        for (int i = 0; i < size; ++i) {
            for (int j = i+1; j < size && (around[j].second - around[i].second)*(around[j].second - around[i].second) < d; j++) {
                long long dist = distance(around[i], around[j]);
                if (dist < d) 
                    d = dist;
            }
        }

    }

    cout << d << endl;

}

/*
8
105 0
100 0
2 0
-2 0
-100 0
-105 0
-1 -1000
1 1000
*/

Test 1

Verdict: ACCEPTED

Test 2

Verdict: TIME LIMIT EXCEEDED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: TIME LIMIT EXCEEDED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: TIME LIMIT EXCEEDED

Test 7

Verdict: WRONG ANSWER

Test 8

Verdict: WRONG ANSWER

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: WRONG ANSWER

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: WRONG ANSWER

Test 15

Verdict: WRONG ANSWER

Test 16

Verdict: TIME LIMIT EXCEEDED

Test 17

Verdict: ACCEPTED

Test 18

Verdict: ACCEPTED