Submission #1333691

#	Time	Username	Problem	Language	Result	Execution time	Memory
1333691		Tony_Tung	Love Polygon (BOI18_polygon)	C++20	100 / 100	143 ms	9336 KiB

polygon

#include <bits/stdc++.h>
#define ll long long
#define ld long double
#define fi first
#define se second
#define pii pair<int, int>
#define all(x) (x).begin(), (x).end()
using namespace std;

const int N = 1e5 + 5;
int nxt[N], in[N];
bool match[N];
map<string, int> mp;

int getId(string &s)
{
    if (mp.find(s) == mp.end()) mp[s] = mp.size();
    return mp[s];
}

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    #define task ""
    if (fopen(task".inp", "r"))
    {
        freopen(task".inp", "r", stdin);
        freopen(task".out", "w", stdout);
    }

    int n; cin >> n;
    for (int i = 1; i <= n; i++)
    {
        string s, t; cin >> s >> t;
        nxt[getId(s)] = getId(t);
    }
    if (n&1)
    {
        cout << -1;
        return 0;
    }
    int cnt0 = 0, cnt1 = 0;
    for (int i = 0; i < n; i++)
    {
        if (!match[i] && nxt[nxt[i]] == i && i != nxt[i])
        {
            match[i] = match[nxt[i]] = 1;
            cnt0++;
        }
    }
    for (int i = 0; i < n; i++)
        if (!match[i]) in[nxt[i]]++;
    queue<int> q;
    for (int i = 0; i < n; i++)
        if (!match[i] && !in[i]) q.push(i);
    while (q.size())
    {
        int u = q.front(); q.pop();
        if (match[u]) continue;
        int v = nxt[u];
        if (!match[v])
        {
            match[u] = match[v] = 1;
            cnt1++;
            int v1 = nxt[v];
            if (!match[v1])
                if (--in[v1] == 0) q.push(v1);
        }
    }
    for (int i = 0; i < n; i++)
    {
        if (!match[i])
        {
            int cur = i, len = 0;
            while (!match[cur])
            {
                match[cur] = 1;
                len++;
                cur = nxt[cur];
            }
            cnt1 += len/2;
        }
    }
    cout << n-2*cnt0-cnt1;

    return 0;
}

Compilation message (stderr)

polygon.cpp: In function 'int main()':
polygon.cpp:28:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   28 |         freopen(task".inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
polygon.cpp:29:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   29 |         freopen(task".out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

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