Problem p04003 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>

#define _overload(_1, _2, _3, name, ...) name
#define _rep(i, n) _range(i, 0, n)
#define _range(i, a, b) for (int i = (int)(a); i < (int)(b); ++i)
#define rep(...) _overload(__VA_ARGS__, _range, _rep, )(__VA_ARGS__)

#define _rrep(i, n) _rrange(i, n, 0)
#define _rrange(i, a, b) for (int i = (int)(a)-1; i >= (int)(b); --i)
#define rrep(...) _overload(__VA_ARGS__, _rrange, _rrep, )(__VA_ARGS__)

#define _all(arg) begin(arg), end(arg)
#define uniq(arg) sort(_all(arg)), (arg).erase(unique(_all(arg)), end(arg))
#define getidx(ary, key) lower_bound(_all(ary), key) - begin(ary)
#define clr(a, b) memset((a), (b), sizeof(a))
#define bit(n) (1LL << (n))

// #define DEBUG

#ifdef DEBUG
#define dump(...) fprintf(stderr, __VA_ARGS__)
#else
#define dump(...)
#endif

template <class T> bool chmax(T &a, const T &b) {
  return (a < b) ? (a = b, 1) : 0;
}
template <class T> bool chmin(T &a, const T &b) {
  return (b < a) ? (a = b, 1) : 0;
}

using namespace std;
using ll = long long;
using vi = vector<int>;
using vll = vector<ll>;

const double EPS = 1e-10;
const double PI = acos(-1.0);
const int inf = INT_MAX;
const ll mod = 1000000007LL;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};

ll extgcd(ll a, ll b, ll &x, ll &y) {
  x = 1, y = 0;
  ll g = a;
  if (b != 0)
    g = extgcd(b, a % b, y, x), y -= a / b * x;
  return g;
}
ll ADD(const ll &a, const ll &b, const ll &mod) { return (a + b) % mod; }
ll SUB(const ll &a, const ll &b, const ll &mod) { return (a - b + mod) % mod; }
ll MUL(const ll &a, const ll &b, const ll &mod) { return (1LL * a * b) % mod; }
ll DIV(const ll &a, const ll &b, const ll &mod) {
  ll x, y;
  extgcd(b, mod, x, y);
  return MUL(a, (x + mod) % mod, mod);
}

random_device rd;
mt19937 mt(rd());
uniform_int_distribution<int> dice(1, 6);
uniform_real_distribution<double> score(0.0, 10.0);

#include <sys/time.h>
double gett() {
  struct timeval t;
  gettimeofday(&t, NULL);
  return t.tv_sec + t.tv_usec / 1e6;
}

int main(void) {
  double st = gett();

  cin.tie(0);
  ios::sync_with_stdio(false);

  int n, m;
  cin >> n >> m;
  using Edge = tuple<int, int>;
  vector<vector<Edge>> G(n);
  rep(loop, m) {
    int a, b, c;
    cin >> a >> b >> c;
    a--, b--;
    G[a].emplace_back(Edge(c, b));
    G[b].emplace_back(Edge(c, a));
  }
  rep(i, n) sort(_all(G[i]));

  using Elem = tuple<int, int, int>;
  priority_queue<Elem, vector<Elem>, greater<Elem>> q;
  int sz = 0;
  vector<unordered_map<int, int>> p2i(n);
  rep(i, n) {
    set<int> s = {0};
    for (auto &e : G[i]) {
      s.insert(get<0>(e));
    }
    for (auto &e : s) {
      p2i[i][e] = sz++;
    }
  }
  vi min_dist(sz, inf);
  q.push(Elem(0, 0, 0));
  min_dist[0] = 0;

  int res = -1;
  while (q.size()) {
    int cost, v, pc;
    tie(cost, v, pc) = q.top();
    q.pop();
    if (cost != min_dist[p2i[v][pc]])
      continue;

    if (v == n - 1) {
      res = cost;
      break;
    }

    if (pc == 0) {
      for (auto &e : G[v]) {
        int nv, nc;
        tie(nv, nc) = e;
        int ncost = cost + 1;
        int idx = p2i[nv][nc];
        if (chmin(min_dist[idx], ncost)) {
          min_dist[idx] = ncost;
          q.push(Elem(ncost, nv, nc));
        }
      }
    } else {
      auto itr = lower_bound(_all(G[v]), Edge(pc, 0));
      while (itr != end(G[v]) and get<0>(*itr) == pc) {
        int nv = get<1>(*itr);
        int nc = pc;
        int ncost = cost;
        int idx = p2i[nv][nc];
        if (chmin(min_dist[idx], ncost)) {
          min_dist[idx] = ncost;
          q.push(Elem(ncost, nv, nc));
        }
        itr++;
      }
    }

    if (pc != 0) {
      int idx = p2i[v][0];
      if (chmin(min_dist[idx], cost)) {
        min_dist[idx] = cost;
        q.push(Elem(cost, v, 0));
      }
    }
  }

  cout << res << endl;

  return 0;
}


Fixed submission:
#include <bits/stdc++.h>

#define _overload(_1, _2, _3, name, ...) name
#define _rep(i, n) _range(i, 0, n)
#define _range(i, a, b) for (int i = (int)(a); i < (int)(b); ++i)
#define rep(...) _overload(__VA_ARGS__, _range, _rep, )(__VA_ARGS__)

#define _rrep(i, n) _rrange(i, n, 0)
#define _rrange(i, a, b) for (int i = (int)(a)-1; i >= (int)(b); --i)
#define rrep(...) _overload(__VA_ARGS__, _rrange, _rrep, )(__VA_ARGS__)

#define _all(arg) begin(arg), end(arg)
#define uniq(arg) sort(_all(arg)), (arg).erase(unique(_all(arg)), end(arg))
#define getidx(ary, key) lower_bound(_all(ary), key) - begin(ary)
#define clr(a, b) memset((a), (b), sizeof(a))
#define bit(n) (1LL << (n))

// #define DEBUG

#ifdef DEBUG
#define dump(...) fprintf(stderr, __VA_ARGS__)
#else
#define dump(...)
#endif

template <class T> bool chmax(T &a, const T &b) {
  return (a < b) ? (a = b, 1) : 0;
}
template <class T> bool chmin(T &a, const T &b) {
  return (b < a) ? (a = b, 1) : 0;
}

using namespace std;
using ll = long long;
using vi = vector<int>;
using vll = vector<ll>;

const double EPS = 1e-10;
const double PI = acos(-1.0);
const int inf = INT_MAX;
const ll mod = 1000000007LL;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};

ll extgcd(ll a, ll b, ll &x, ll &y) {
  x = 1, y = 0;
  ll g = a;
  if (b != 0)
    g = extgcd(b, a % b, y, x), y -= a / b * x;
  return g;
}
ll ADD(const ll &a, const ll &b, const ll &mod) { return (a + b) % mod; }
ll SUB(const ll &a, const ll &b, const ll &mod) { return (a - b + mod) % mod; }
ll MUL(const ll &a, const ll &b, const ll &mod) { return (1LL * a * b) % mod; }
ll DIV(const ll &a, const ll &b, const ll &mod) {
  ll x, y;
  extgcd(b, mod, x, y);
  return MUL(a, (x + mod) % mod, mod);
}

random_device rd;
mt19937 mt(rd());
uniform_int_distribution<int> dice(1, 6);
uniform_real_distribution<double> score(0.0, 10.0);

#include <sys/time.h>
double gett() {
  struct timeval t;
  gettimeofday(&t, NULL);
  return t.tv_sec + t.tv_usec / 1e6;
}

int main(void) {
  double st = gett();

  cin.tie(0);
  ios::sync_with_stdio(false);

  int n, m;
  cin >> n >> m;
  using Edge = tuple<int, int>;
  vector<vector<Edge>> G(n);
  rep(loop, m) {
    int a, b, c;
    cin >> a >> b >> c;
    a--, b--;
    G[a].emplace_back(Edge(c, b));
    G[b].emplace_back(Edge(c, a));
  }
  rep(i, n) sort(_all(G[i]));

  using Elem = tuple<int, int, int>;
  priority_queue<Elem, vector<Elem>, greater<Elem>> q;
  int sz = 0;
  vector<unordered_map<int, int>> p2i(n);
  rep(i, n) {
    set<int> s = {0};
    for (auto &e : G[i]) {
      s.insert(get<0>(e));
    }
    for (auto &e : s) {
      p2i[i][e] = sz++;
    }
  }
  vi min_dist(sz, inf);
  q.push(Elem(0, 0, 0));
  min_dist[0] = 0;

  int res = -1;
  while (q.size()) {
    int cost, v, pc;
    tie(cost, v, pc) = q.top();
    q.pop();
    if (cost != min_dist[p2i[v][pc]])
      continue;

    if (v == n - 1) {
      res = cost;
      break;
    }

    if (pc == 0) {
      for (auto &e : G[v]) {
        int nv, nc;
        tie(nc, nv) = e;
        int ncost = cost + 1;
        int idx = p2i[nv][nc];
        if (chmin(min_dist[idx], ncost)) {
          min_dist[idx] = ncost;
          q.push(Elem(ncost, nv, nc));
        }
      }
    } else {
      auto itr = lower_bound(_all(G[v]), Edge(pc, 0));
      while (itr != end(G[v]) and get<0>(*itr) == pc) {
        int nv = get<1>(*itr);
        int nc = pc;
        int ncost = cost;
        int idx = p2i[nv][nc];
        if (chmin(min_dist[idx], ncost)) {
          min_dist[idx] = ncost;
          q.push(Elem(ncost, nv, nc));
        }
        itr++;
      }
    }

    if (pc != 0) {
      int idx = p2i[v][0];
      if (chmin(min_dist[idx], cost)) {
        min_dist[idx] = cost;
        q.push(Elem(cost, v, 0));
      }
    }
  }

  cout << res << endl;

  return 0;
}