Submission #8536909

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Source Code Expand

/**
 *    author:  tourist
 *    created: 20.11.2019 08:57:54       
**/
#include <bits/stdc++.h>

using namespace std;

class matching {
 public:
  vector<vector<int>> g;
  vector<int> pa;
  vector<int> pb;
  vector<int> was;
  int n, m;
  int res;
  int iter;

  matching(int _n, int _m) : n(_n), m(_m) {
    assert(0 <= n && 0 <= m);
    pa = vector<int>(n, -1);
    pb = vector<int>(m, -1);
    was = vector<int>(n, 0);
    g.resize(n);
    res = 0;
    iter = 0;
  }

  void add(int from, int to) {
    assert(0 <= from && from < n && 0 <= to && to < m);
    g[from].push_back(to);
  }

  bool dfs(int v) {
    was[v] = iter;
    for (int u : g[v]) {
      if (pb[u] == -1) {
        pa[v] = u;
        pb[u] = v;
        return true;
      }
    }
    for (int u : g[v]) {
      if (was[pb[u]] != iter && dfs(pb[u])) {
        pa[v] = u;
        pb[u] = v;
        return true;
      }
    }
    return false;
  }

  int solve() {
    while (true) {
      iter++;
      int add = 0;
      for (int i = 0; i < n; i++) {
        if (pa[i] == -1 && dfs(i)) {
          add++;
        }
      }
      if (add == 0) {
        break;
      }
      res += add;
    }
    return res;
  }

  int run_one(int v) {
    if (pa[v] != -1) {
      return 0;
    }
    iter++;
    return (int) dfs(v);
  }
};

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  const int N = (int) 1e7 + 10;
  vector<bool> prime(N, true);
  for (int i = 2; i < N; i++) if (prime[i]) for (int j = i + i; j < N; j += i) prime[j] = false;
  prime[1] = false;
  int n;
  cin >> n;
  map<int, int> mp;
  for (int i = 0; i < n; i++) {
    int x;
    cin >> x;
    mp[x] ^= 1;
    mp[x + 1] ^= 1;
  }
  vector<int> x, y;
  for (auto& p : mp) {
    if (p.second == 1) {
      if (p.first % 2 == 0) x.push_back(p.first);
      else y.push_back(p.first);
    }
  }
  int xn = (int) x.size();
  int yn = (int) y.size();
  matching mat(xn, yn);
  for (int i = 0; i < xn; i++) {
    for (int j = 0; j < yn; j++) {
      if (prime[abs(x[i] - y[j])]) {
        mat.add(i, j);
      }
    }
  }
  int u = mat.solve();
  int ans = u;
  xn -= u;
  yn -= u;
  ans += xn / 2 * 2;
  ans += yn / 2 * 2;
  if (xn % 2 == 1) {
    ans += 3;
  }
  cout << ans << '\n';
  return 0;
}

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