Line Intersections

// ~/.vim/cpp_template.cpp
#include <bits/stdc++.h>
#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
#include <limits>

#define REP(i,a,b) for (int i = a; i < b; i++)

// Type Aliases for 1D and 2D vectors with initialization
#define vi(n, val) vector<int>(n, val) // 1D vector of ints with size n, initialized to val
#define vll(n, val) vector<long long>(n, val) // 1D vector of long longs with size n, initialized to val
#define ll long long
#define vvi(n, m, val) vector<vector<int>>(n, vector<int>(m, val)) // 2D vector of ints (n x m), initialized to val
#define vvll(n, m, val) vector<vector<long long>>(n, vector<long long>(m, val)) // 2D vector of long longs (n x m), initialized to val

#define LL_INF std::numeric_limits<long long int>::max()
#define INF std::numeric_limits<int>::max()


using namespace std;


template <typename T>
void pV(const std::vector<T>& vec, const std::string& label = "Vector") {
    std::cout << label << ": [ ";
    for (const auto& elem : vec) {
        std::cout << elem << " ";
    }
    std::cout << "]" << std::endl;
}


void dfs(int s, vector<bool> *visited, vector<int> (*adj)[]) {
    if ((*visited)[s]) return;
    (*visited)[s] = true;
    // process node s


    for (auto u: (*adj)[s]) {
        dfs(u, visited, adj);
    }
}
/*
// DEPTH-FRIRST-SEARCH
vector<int> adj[N];                                                          
vector<bool> visited(N, false);
int u, v;
for(int i = 0; i < M;i++){
    cin >> u >> v;
    u--;
    v--;
    adj[u].push_back(v);
    adj[v].push_back(u);
}
*/

vector<long long> dijkstra(int N, int x, vector<vector<pair<int,int>>> *adj){
    vector<bool> processed(N, false);
    vector<long long> distance(N, LL_INF);
    priority_queue<pair<long long,int>> q;
    //for (int i = 1; i <= n; i++) distance[i] = INF;
    distance[x] = 0;
    q.push({0,x});
    while (!q.empty()) {
        int a = q.top().second; q.pop();
        if (processed[a]) continue;
        processed[a] = true;
        for (auto u : (*adj)[a]) {
            int b = u.first, w = u.second;
            if (distance[a]+w < distance[b]) {
                distance[b] = distance[a]+w;
                q.push({-distance[b],b});
            }
        }
    }
    return distance;


}


/*
DIJKSTRA
//vector<vector<pair<int,int>>> adj(N, vector<pair<int, int>>(N));
*/



struct Event {
    int x, type, y1, y2;
    bool operator<(const Event& other) const {
        return x < other.x || (x == other.x && type < other.type);
    }
};

class SegmentTree {
public:
    SegmentTree(int size) {
        this->size = size;
        tree.assign(4 * size, 0);
    }

    void add(int node, int start, int end, int idx, int val) {
        if (start == end) {
            tree[node] += val;
        } else {
            int mid = (start + end) / 2;
            if (idx <= mid) add(2 * node, start, mid, idx, val);
            else add(2 * node + 1, mid + 1, end, idx, val);
            tree[node] = tree[2 * node] + tree[2 * node + 1];
        }
    }

    int query(int node, int start, int end, int l, int r) {
        if (r < start || end < l) return 0;
        if (l <= start && end <= r) return tree[node];
        int mid = (start + end) / 2;
        return query(2 * node, start, mid, l, r) + query(2 * node + 1, mid + 1, end, l, r);
    }

private:
    int size;
    vector<int> tree;
};

int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    // Your code starts here
    int n;
    cin >> n;

    vector<Event> events;
    set<int> y_coords;

    REP(i, 0, n){
        int x1, y1, x2, y2;
        cin >> x1 >> y1 >> x2 >> y2;

        if (x1 == x2) {
            if (y1 > y2) swap(y1, y2);
            events.push_back({x1, 2, y1, y2});
        } else {
            if (x1 > x2) swap(x1, x2);
            events.push_back({x1, 1, y1, y1});
            events.push_back({x2, -1, y1, y1});
            y_coords.insert(y1);
        }
    }

    map<int, int> compress;
    int idx = 0;
    for (int y : y_coords) {
        compress[y] = idx++;
    }

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

    SegmentTree seg_tree(idx);

    int intersections = 0;
    for (const Event& e : events) {
        if (e.type == 1) {
            seg_tree.add(1, 0, idx - 1, compress[e.y1], 1);
        } else if (e.type == -1) {
            seg_tree.add(1, 0, idx - 1, compress[e.y1], -1);
        } else {
            intersections += seg_tree.query(1, 0, idx - 1, compress[e.y1], compress[e.y2]);
        }
    }

    cout << intersections << endl;
    return 0;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: WRONG ANSWER

Test 7

Verdict: ACCEPTED

Test 8

Verdict: WRONG ANSWER

Test 9

Verdict: ACCEPTED

Test 10

Verdict: WRONG ANSWER

Test 11

Verdict: WRONG ANSWER

Test 12

Verdict: WRONG ANSWER

Test 13

Verdict: WRONG ANSWER

Test 14

Verdict: ACCEPTED

Test 15

Verdict: WRONG ANSWER

Test 16

Verdict: WRONG ANSWER

Test 17

Verdict: WRONG ANSWER

Test 18

Verdict: WRONG ANSWER

Test 19

Verdict: WRONG ANSWER

Test 20

Verdict: WRONG ANSWER

Test 21

Verdict: WRONG ANSWER

Test 22

Verdict: WRONG ANSWER

Test 23

Verdict: WRONG ANSWER

Test 24

Verdict: WRONG ANSWER

Test 25

Verdict: WRONG ANSWER

Test 26

Verdict: WRONG ANSWER

Test 27

Verdict: WRONG ANSWER

Test 28

Verdict: WRONG ANSWER

Test 29

Verdict: WRONG ANSWER

Test 30

Verdict: WRONG ANSWER

Test 31

Verdict: WRONG ANSWER

Test 32

Verdict: WRONG ANSWER

Test 33

Verdict: WRONG ANSWER

Test 34

Verdict: WRONG ANSWER

Test 35

Verdict: WRONG ANSWER

Test 36

Verdict: WRONG ANSWER

Test 37

Verdict: WRONG ANSWER

Test 38

Verdict: WRONG ANSWER

Test 39

Verdict: WRONG ANSWER

Test 40

Verdict: WRONG ANSWER