Problem p00876 (C++) — buggy submission, verdict: Time Limit Exceeded

#define __USE_MINGW_ANSI_STDIO 0
#include <bits/stdc++.h>

using namespace std;
using ll = long long;
#define int ll
using VI = vector<int>;
using VVI = vector<VI>;
using PII = pair<int, int>;

#define FOR(i, a, n) for (ll i = (ll)a; i < (ll)n; ++i)
#define REP(i, n) FOR(i, 0, n)
#define ALL(x) x.begin(), x.end()
#define PB push_back

const ll LLINF = (1LL << 60);
const int INF = (1LL << 30);
const int MOD = 1000000007;

template <typename T> T &chmin(T &a, const T &b) { return a = min(a, b); }
template <typename T> T &chmax(T &a, const T &b) { return a = max(a, b); }
template <typename T> bool IN(T a, T b, T x) { return a <= x && x < b; }
template <typename T> T ceil(T a, T b) { return a / b + !!(a % b); }
template <class S, class T>
ostream &operator<<(ostream &out, const pair<S, T> &a) {
  out << '(' << a.first << ',' << a.second << ')';
  return out;
}
template <class T> ostream &operator<<(ostream &out, const vector<T> &a) {
  out << '[';
  REP(i, a.size()) {
    out << a[i];
    if (i != a.size() - 1)
      out << ',';
  }
  out << ']';
  return out;
}

int dx[] = {0, 1, 0, -1}, dy[] = {1, 0, -1, 0};

signed main(void) {
  cin.tie(0);
  ios::sync_with_stdio(false);

  while (true) {
    int n;
    cin >> n;
    if (!n)
      break;
    VI t(n), c(n);
    vector<PII> p(n);
    REP(i, n) {
      cin >> t[i] >> c[i];
      p[i] = {t[i], i};
    }
    sort(ALL(p));

    // (人i, 折り返すまでにかかる時間, 周回数)
    queue<VI> que[2];
    REP(i, n) que[0].push({p[i].second, p[i].first, 0});

    int ans = 0;
    while (que[0].size() || que[1].size()) {
      // curのqueueから取り出す
      int cur = 0;
      if (que[cur].empty())
        cur ^= 1;
      else if (que[cur ^ 1].size() &&
               que[cur].front()[1] > que[cur ^ 1].front()[1])
        cur ^= 1;

      // next以下のものを取り出す
      VVI v;
      int next = que[cur].front()[1];
      while (que[cur].size() && que[cur].front()[1] <= next) {
        v.PB(que[cur].front());
        que[cur].pop();
      }
      // vの中身を速度順でソートする
      sort(ALL(v), [&](const VI &a, const VI &b) { return t[a[0]] < t[b[0]]; });
      // vの中身を次のqueueに移す
      REP(i, v.size()) {
        if (cur == 1)
          v[i][2]++;
        if (v[i][2] == c[v[i][0]])
          ans = next;
        else
          que[cur ^ 1].push({v[i][0], next + t[v[i][0]], v[i][2]});
      }
    }
    cout << ans << endl;
  }

  return 0;
}


Error: TLE

Fixed submission:

#define __USE_MINGW_ANSI_STDIO 0
#include <bits/stdc++.h>

using namespace std;
using ll = long long;
#define int ll
using VI = vector<int>;
using VVI = vector<VI>;
using PII = pair<int, int>;

#define FOR(i, a, n) for (ll i = (ll)a; i < (ll)n; ++i)
#define REP(i, n) FOR(i, 0, n)
#define ALL(x) x.begin(), x.end()
#define PB push_back

const ll LLINF = (1LL << 60);
const int INF = (1LL << 30);
const int MOD = 1000000007;

template <typename T> T &chmin(T &a, const T &b) { return a = min(a, b); }
template <typename T> T &chmax(T &a, const T &b) { return a = max(a, b); }
template <typename T> bool IN(T a, T b, T x) { return a <= x && x < b; }
template <typename T> T ceil(T a, T b) { return a / b + !!(a % b); }
template <class S, class T>
ostream &operator<<(ostream &out, const pair<S, T> &a) {
  out << '(' << a.first << ',' << a.second << ')';
  return out;
}
template <class T> ostream &operator<<(ostream &out, const vector<T> &a) {
  out << '[';
  REP(i, a.size()) {
    out << a[i];
    if (i != a.size() - 1)
      out << ',';
  }
  out << ']';
  return out;
}

int dx[] = {0, 1, 0, -1}, dy[] = {1, 0, -1, 0};

signed main(void) {
  cin.tie(0);
  ios::sync_with_stdio(false);

  while (true) {
    double EPS = 1e-8;
    double length = 1e6;
    int n;
    cin >> n;
    if (!n)
      break;
    VI t(n), c(n);
    vector<PII> p(n);
    REP(i, n) {
      cin >> t[i] >> c[i];
      p[i] = pair<double, int>{t[i], c[i]};
    }
    sort(ALL(p));

    // i人目の人の速度
    vector<double> v(n);
    REP(i, n) v[i] = length / p[i].first;

    // i人目の人の位置、何周目か
    vector<pair<double, int>> place(n, {0, 0});
    vector<pair<double, int>> nxt(n, {0, 0});
    int i, num;
    for (i = 0, num = 0; num < n; ++i) {
      // j人目を進める
      REP(j, n) {
        if (place[j].second >= c[j])
          continue;
        double tmp = place[j].first + v[j];
        REP(k, n) {
          if (j == k)
            continue;
          if (place[k].second >= p[k].second)
            continue;
          if (place[j].first < EPS && place[k].first < EPS)
            continue;
          if (abs(place[j].first - length) < EPS &&
              abs(place[k].first - length) < EPS)
            continue;
          // jがkを追い越す
          if (place[j].first <= place[k].first &&
              place[j].first + v[j] > place[k].first + v[k]) {
            chmin(tmp, place[k].first + v[k]);
          }
        }
        if (place[j].first < 2 * length && 2 * length <= tmp + EPS) {
          nxt[j] = pair<double, int>{0, place[j].second + 1};
          if (nxt[j].second >= p[j].second)
            num++;
        } else {
          nxt[j] = pair<double, int>{tmp, place[j].second};
        }
      }
      place = nxt;
      // cout << place << endl;
    }

    cout << i << endl;
  }

  return 0;
}