AcWing 372. 棋盘覆盖

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

using namespace std;
int n, t, a, b, g[A], ans; bool vis[A], w[A];
vector<int> v[A];
bool check(int x) {
  if (w[x]) return false;
  for (auto i : v[x]) {
    if (!vis[i] and !w[i]) {
      vis[i] = 1;
      if (!g[i] or check(g[i])) {
        g[i] = x;
        return true;
      }
    }
  }
  return false;
}

int main(int argc, char const *argv[]) {
  cin >> n >> t;
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= n; j++)
      if ((i + j) % 2) {
        int pos = (i - 1) * n + j;
        if (i - 1 >= 1) v[pos].push_back((i - 2) * n + j);
        if (i + 1 <= n) v[pos].push_back(i * n + j);
        if (j - 1 >= 1) v[pos].push_back((i - 1) * n + j - 1);
        if (j + 1 <= n) v[pos].push_back((i - 1) * n + j + 1);
      }
  for (int i = 1; i <= t; i++) scanf("%d%d", &a, &b), w[n * (a - 1) + b] = 1;
  for (int i = 1; i <= n * n; i++) {
    memset(vis, 0, sizeof vis);
    if (check(i)) ans++;
  }
  cout << ans << endl;
}