Submission #51850

#	Time	Username	Problem	Language	Result	Execution time	Memory
51850		mareksom	Network (BOI15_net)	C++17	100 / 100	1772 ms	210956 KiB

net

#ifndef LOCAL
#pragma GCC optimize ("O3")
#endif

#include <bits/stdc++.h>

using namespace std;

#define sim template < class c
#define ris return * this
#define dor > debug & operator <<
#define eni(x) sim > typename \
enable_if<sizeof dud<c>(0) x 1, debug&>::type operator<<(c i) {
sim > struct rge { c b, e; };
sim > rge<c> range(c i, c j) { return {i, j}; }
sim > auto dud(c* x) -> decltype(cerr << *x, 0);
sim > char dud(...);
struct debug {
#ifdef LOCAL
~debug() { cerr << endl; }
eni(!=) cerr << boolalpha << i; ris; }
eni(==) ris << range(begin(i), end(i)); }
sim, class b dor(pair < b, c > d) {
  ris << "(" << d.first << ", " << d.second << ")";
}
sim dor(rge<c> d) {
  *this << "[";
  for (c it = d.b; it != d.e; ++it)
    *this << ", " + 2 * (it == d.b) << *it;
  ris << "]";
}
#else
sim dor(const c&) { ris; }
#endif
};
#define imie(x...) " [" #x ": " << (x) << "] "

using ld = long double;
using ll = long long;

constexpr int mod = 1000 * 1000 * 1000 + 7;
constexpr int odw2 = (mod + 1) / 2;

void OdejmijOd(int& a, int b) { a -= b; if (a < 0) a += mod; }
int Odejmij(int a, int b) { OdejmijOd(a, b); return a; }
void DodajDo(int& a, int b) { a += b; if (a >= mod) a -= mod; }
int Dodaj(int a, int b) { DodajDo(a, b); return a; }
int Mnoz(int a, int b) { return (ll) a * b % mod; }
void MnozDo(int& a, int b) { a = Mnoz(a, b); }
int Pot(int a, int b) { int res = 1; while (b) { if (b % 2 == 1) MnozDo(res, a); a = Mnoz(a, a); b /= 2; } return res; }
int Odw(int a) { return Pot(a, mod - 2); }
void PodzielDo(int& a, int b) { MnozDo(a, Odw(b)); }
int Podziel(int a, int b) { return Mnoz(a, Odw(b)); }
int Moduluj(ll x) { x %= mod; if (x < 0) x += mod; return x; }

template <typename T> T Maxi(T& a, T b) { return a = max(a, b); }
template <typename T> T Mini(T& a, T b) { return a = min(a, b); }

constexpr int nax = 500 * 1000 + 105;

int n;
set<int> graf[nax];
vector<pair<int, int>> wynik;

int Daj(int x, int oprocz) {
  assert(!graf[x].empty());
  if (graf[x].find(oprocz) == graf[x].end()) {
    if ((int) graf[x].size() >= 2) return -1;
    return *graf[x].begin();
  }
  if ((int) graf[x].size() >= 3) return -1;
  for (int y : graf[x]) {
    if (y != oprocz) {
      return y;
    }
  }
  assert(false);
}

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cin >> n;
  for (int i = 1; i < n; i++) {
    int a, b;
    cin >> a >> b;
    graf[a].insert(b);
    graf[b].insert(a);
  }
  set<int> liscie;
  for (int i = 1; i <= n; i++) {
    if ((int) graf[i].size() == 1) {
      liscie.insert(i);
    }
  }
  debug() << imie(liscie);
  while (true) {
    assert((int) liscie.size() >= 2);
    const int a = *liscie.begin();
    liscie.erase(liscie.begin());
    const int b = *liscie.begin();
    liscie.erase(*liscie.begin());
    if ((int) liscie.size() <= 1) {
      wynik.emplace_back(a, b);
      liscie.insert(b);
      if ((int) liscie.size() < 2) break;
      continue;
    }
    const int c = *liscie.begin();
    liscie.erase(liscie.begin());
    int s[3] = {a, b, c};
    int w[3] = {a, b, c};
    int p[3] = {-1, -1, -1};
    while (true) {
      int daj[3];
      for (int i = 0; i < 3; i++) {
        daj[i] = Daj(w[i], p[i]);
      }
      debug() << imie(range(s, s + 3));
      debug() << imie(range(w, w + 3));
      debug() << imie(range(p, p + 3));
      debug() << imie(range(daj, daj + 3));
      for (int i = 0; i < 3; i++) {
        for (int j = i + 1; j < 3; j++) {
          if (daj[i] == -1 and daj[j] == -1) {
            if (w[i] != w[j] or (int) graf[w[i]].size() >= 4) {
              debug() << imie("JEST");
              wynik.emplace_back(s[i], s[j]);
              liscie.insert(s[3 ^ i ^ j]);
              graf[w[i]].erase(p[i]);
              graf[w[j]].erase(p[j]);
              goto out;
            }
          }
        }
      }
      for (int i = 0; i < 3; i++) {
        if (daj[i] != -1) {
          p[i] = w[i];
          w[i] = daj[i];
        }
      }
    }
    out:;
  }
  printf("%d\n", (int) wynik.size());
  for (auto& it : wynik) {
    printf("%d %d\n", it.first, it.second);
  }
  return 0;
}

• Subtask 1: 18 / 18
• Subtask 2: 45 / 45
• Subtask 3: 37 / 37