Submission #924367

#	Time	Username	Problem	Language	Result	Execution time	Memory
924367		aykhn	Love Polygon (BOI18_polygon)	C++17	29 / 100	155 ms	24400 KiB

polygon

#include <bits/stdc++.h>
// author: aykhn
using namespace std;
#define int long long
#define inf 0x3F3F3F3F
 
const int MXN = 1e5 + 5;
 
int n;
vector<int> adj[MXN];
map<string, int> mp;
int to[MXN], dp[MXN][2];
 
void dfs(int a)
{
    if (adj[a].empty())
    {
        dp[a][0] = dp[a][1] = 1;
        return;
    }
    dp[a][0] = 0;
    dp[a][1] = inf;
    for (int v : adj[a])
    {
        dfs(v);
        dp[a][0] += min(dp[v][0], dp[v][1]);
    }
    for (int v : adj[a])
    {
        dp[a][1] = min(dp[a][1], dp[a][0] - min(dp[v][0], dp[v][1]) + dp[v][0] - 1);
    }
    dp[a][0]++;
    assert(dp[a][1] <= dp[a][0]);
}
 
signed main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(nullptr);
    int n, m = 0;
    cin >> n;
    if (n & 1)
    {
        cout << -1 << '\n';
        return 0;
    }
    for (int i = 1; i <= n; i++)
    {
        string a, b;
        cin >> a >> b;
        if (mp.find(a) == mp.end()) mp[a] = ++m;
        if (mp.find(b) == mp.end()) mp[b] = ++m;
        to[mp[a]] = mp[b];
    }
    vector<int> r;
    for (int i = 1; i <= m; i++)
    {
        if (to[i] == i) r.push_back(i);
        if (to[to[i]] == i) continue;
        adj[to[i]].push_back(i);
    }
    int res = 0;
    for (int i : r)
    {
        dfs(i);
        res += min(dp[i][0], dp[i][1]);
    }
    cout << (n + res)/2 << '\n';
}

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