Submission #442537

#	Time	Username	Problem	Language	Result	Execution time	Memory
442537		abc864197532	Love Polygon (BOI18_polygon)	C++17	100 / 100	333 ms	38476 KiB

polygon

#include <bits/stdc++.h>
using namespace std;
#define lli long long int
#define X first
#define Y second
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define pii pair<int, int>
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define test(args...) abc("[" + string(#args) + "]", args)
void abc() {cerr << endl;}
template <typename T, typename ...U> void abc(T a, U ...b) {
    cerr << a << ' ', abc(b...);
}
template <typename T> void printv(T l, T r) {
    while (l != r) cerr << *l << " \n"[++l == r];
}
const int mod = 1e9 + 7, N = 200000;

int dsu[N];

int Find(int x) {
    if (x == dsu[x]) return x;
    return dsu[x] = Find(dsu[x]);
}

bool Union(int u, int v) {
    u = Find(u), v = Find(v);
    if (u == v) return false;
    dsu[u] = v;
    return true;
}

int main () {
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n, _id = 0;
    cin >> n;
    if (n & 1) return cout << -1 << endl, 0;
    map <string, int> m1;
    auto get = [&](string s) {
        if (m1.count(s)) return m1[s];
        return m1[s] = _id++;
    };
    for (int i = 0; i < n; ++i) dsu[i] = i;
    vector <vector <int>> adj(n);
    vector <int> pt(n);
    string s, t;
    vector <pii> oth;
    for (int i = 0; i < n; ++i) {
        cin >> s >> t;
        int u = get(s), v = get(t);
        pt[u] = v;
        if (Union(u, v)) adj[v].pb(u), adj[u].pb(v);
        else oth.eb(v, u);
    }
    vector <int> cur;
    vector <vector <int>> dp1(n, vector <int>(2, 0));
    vector <vector <int>> dp2(n, vector <int>(2, 0));
    // 0 not choose, 1 choose
    vector <bool> vis(n, false);
    int cnt = 0;
    function<void(int, int, int)> dfs = [&](int v, int pa, int out) {
        cnt++;
        for (int u : adj[v]) if (u != pa) {
            dfs(u, v, out);
            dp1[v][0] += max(dp1[u][0], dp1[u][1]);
            dp2[v][0] += max(dp2[u][0], dp2[u][1]);
        }
        for (int u : adj[v]) if (u != pa) {
            dp1[v][1] = max(dp1[v][1], dp1[v][0] - max(dp1[u][0], dp1[u][1]) + dp1[u][0] + 1);
            if (u != out) dp2[v][1] = max(dp2[v][1], dp2[v][0] - max(dp2[u][0], dp2[u][1]) + dp2[u][0] + 1);
        }
        if (v == out) dp2[v][1] = -1 << 30;
    };
    int ans = n;
    for (pii A : oth) {
        cnt = 0;
        dfs(A.X, -1, A.Y);
        if (A.X != A.Y) ans -= max({dp1[A.X][0], dp1[A.X][1], dp2[A.X][0] + (pt[A.X] == A.Y && pt[A.Y] == A.X ? 2 : 1)});
        else ans -= max(dp1[A.X][0], dp1[A.X][1]);
    }
    cout << ans << endl;
}

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