Submission #696562

#	Time	Username	Problem	Language	Result	Execution time	Memory
696562		mdbrnowski	Love Polygon (BOI18_polygon)	C++17	54 / 100	299 ms	20100 KiB

polygon

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

typedef vector<int> vi;

int cycle_length(int i, int start, vi& graph, vector<bool>& visited, int length) {
    visited[i] = true;
    if (i == start) return length;
    else return cycle_length(graph[i], start, graph, visited, length+1);
}

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int n;
    cin >> n;
    map<string,int> names;
    int cur_name = 0;
    vi graph(n);
    vector<set<int>> rgraph(n);
    for (int i = 0; i < n; i++) {
        string a, b;
        cin >> a >> b;
        if (names.find(a) == names.end()) names[a] = cur_name++;
        if (names.find(b) == names.end()) names[b] = cur_name++;

        if (names[a] == names[b])
            graph[names[a]] = -1;
        else {
            graph[names[a]] = names[b];
            rgraph[names[b]].insert(names[a]);
        }
    }
    if (n & 1) {
        cout << -1 << '\n';
        return 0;
    }
    int res = 0;
    queue<int> q;
    for (int i = 0; i < n; i++)
        if (rgraph[i].size() == 0)
            q.push(i);
    while (q.size()) {
        int u = q.front(); q.pop();
        int v = graph[u];
        if (v == -1)
            continue;
        res++;
        for (auto x : rgraph[v])
            if (x != u)
                graph[x] = -1;
        int w = graph[v];
        if (w > -1) {
            rgraph[w].erase(rgraph[w].find(v));
            if (rgraph[w].size() == 0)
                q.push(w);
        }
        graph[v] = u;
    }

    vector<bool> visited(n, false);
    for (int i = 0; i < n; i++) {
        if (visited[i]) continue;
        visited[i] = true;
        if (graph[i] == -1) res++;
        else {
            int c = cycle_length(graph[i], i, graph, visited, 1);
            if (c > 2)
                res += (c + 1) / 2;
        }
    }

    cout << res << '\n';
    return 0;
}

• Subtask 1: 0 / 21
• Subtask 2: 25 / 25
• Subtask 3: 29 / 29
• Subtask 4: 0 / 25