Submission #1333728

#	Time	Username	Problem	Language	Result	Execution time	Memory
1333728		Hduong	Love Polygon (BOI18_polygon)	C++20	25 / 100	27 ms	11036 KiB

polygon

#include <bits/stdc++.h>
#define task "task"

using namespace std;

const int N = 200005;
const int HASH_SIZE = 199999;

long long n, love[N], in_degree[N];
bool matched[N];

struct node {
  string key;
  long long val;
  node* next;
};

node* head[HASH_SIZE];
long long cnt = 1;

long long get_id(string s) {
  unsigned long long h = 0;
  for (char c : s) h = h * 31 + c;
  int idx = h % HASH_SIZE;

  node* curr = head[idx];
  while (curr != nullptr) {
    if (curr->key == s) return curr->val;
    curr = curr->next;
  }

  node* newnode = new node();
  newnode->key = s;
  newnode->val = cnt++;
  newnode->next = head[idx];
  head[idx] = newnode;
  return newnode->val;
}

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);

  if (fopen(task".inp", "r")) {
    freopen(task".inp", "r", stdin);
    freopen(task".out", "w", stdout);
  }

  cin >> n;
  if (n % 2 != 0) {
    cout << -1;
    return 0;
  }

  for (int i = 1; i <= n; i++) {
    string u_s, v_s;
    cin >> u_s >> v_s;
    long long u = get_id(u_s), v = get_id(v_s);
    love[u] = v;
    in_degree[v]++;
  }

  long long res = 0;

  for (int i = 1; i <= n; i++) {
    if (!matched[i]) {
      int j = love[i];
      if (i != j && love[j] == i && !matched[j]) {
        matched[i] = true;
        matched[j] = true;
      }
    }
  }

  queue<long long> q;
  for (int i = 1; i <= n; i++) {
    if (in_degree[i] == 0) q.push(i);
  }

  while (!q.empty()) {
    long long u = q.front();
    q.pop();
    if (matched[u]) continue;

    long long v = love[u];
    if (!matched[v]) {
      matched[u] = true;
      matched[v] = true;
      res += 1;
    }

    in_degree[v]--;
    if (in_degree[v] == 0) q.push(v);
  }

  for (int i = 1; i <= n; i++) {
    if (!matched[i]) {
      long long curr = i, siz = 0;
      vector<long long> nodes;
      while (!matched[curr]) {
        matched[curr] = true;
        nodes.push_back(curr);
        curr = love[curr];
        siz++;
      }

      if (siz >= 2 && love[nodes.back()] == nodes[0]) {
        res += (siz / 2);
        if (siz % 2 != 0) {
          matched[nodes.back()] = false;
        }
      } else {
        for (int k = 0; k < nodes.size(); k++) {
          matched[nodes[k]] = false;
        }
      }
    }
  }

  long long tmp = 0;
  for (int i = 1; i <= n; i++) {
    if (!matched[i]) tmp++;
  }
  res += tmp;

  cout << res;
}

Compilation message (stderr)

polygon.cpp: In function 'int main()':
polygon.cpp:45:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   45 |     freopen(task".inp", "r", stdin);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
polygon.cpp:46:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   46 |     freopen(task".out", "w", stdout);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

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