Problem p00743 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <algorithm>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <string>
#include <vector>
using namespace std;

#define REP(i, n) for (int i = 0; i < (int)n; ++i)
#define FOR(i, c)                                                              \
  for (__typeof((c).begin()) i = (c).begin(); i != (c).end(); ++i)
#define ALL(c) (c).begin(), (c).end()
const int INF = 1 << 29;

typedef double Weight;
struct Edge {
  int src, dst;
  Weight weight;
  int c; // c ÍOtÅÍ§À¬xAqueue ÅÍ¬x
  Edge(int src, int dst, Weight weight, int c)
      : src(src), dst(dst), weight(weight), c(c) {}
};

bool operator<(const Edge &e, const Edge &f) {
  return e.weight != f.weight ? e.weight > f.weight : // !!INVERSE!!
             e.src != f.src ? e.src < f.src
         : e.dst != f.dst   ? e.dst < f.dst
                            : e.c < f.c;
}

typedef vector<Edge> Edges;
typedef vector<Edges> Graph;
typedef pair<int, int> pii;

double dist[30][30][32]; // dist[i][j][k] = Xs[h k ÌóÔÅ j ©ç
                         // i ÉÂ­ÅZ£

double dijkstra(const Graph &g, int s, int t) {
  int n = g.size();
  REP(i, n) REP(j, n) REP(k, 32) dist[i][j][k] = INF;
  priority_queue<Edge> Q;
  Q.push(Edge(s, s, 0, 0));
  int cnt = 0;
  while (!Q.empty()) {
    Edge e = Q.top();
    Q.pop();
    if (e.dst == t && e.c == 1)
      break;
    REP(k, 3) {
      int v = e.c - 1 + k;
      if (v <= 0)
        continue;
      if (dist[e.dst][e.src][v] < e.weight)
        continue;
      FOR(f, g[e.dst]) {
        if (v > f->c)
          continue;
        if (f->dst == e.src)
          continue;
        double hoge = e.weight + f->weight / v;
        if (dist[f->dst][f->src][v] > hoge) {
          dist[f->dst][f->src][v] = hoge;
          Q.push(Edge(f->src, f->dst, hoge, v));
        }
      }
    }
    if (cnt++ > 1000000)
      break;
  }

  double res = INF;
  REP(i, n)
  res = min(res, dist[t][i][1]);
  return res;
}

int main() {
  int n, m;
  while (cin >> n >> m, n || m) {
    int s, t;
    cin >> s >> t;
    s--;
    t--;
    Graph g(n);
    REP(i, m) {
      int x, y, d, c;
      cin >> x >> y >> d >> c;
      x--;
      y--;
      g[x].push_back(Edge(x, y, d, c));
      g[y].push_back(Edge(y, x, d, c));
    }
    double res = dijkstra(g, s, t);
    if (res == INF)
      cout << "unreachable" << endl;
    else
      printf("%.5f\n", res);
  }
}

Fixed submission:
#include <algorithm>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <string>
#include <vector>
using namespace std;

#define REP(i, n) for (int i = 0; i < (int)n; ++i)
#define FOR(i, c)                                                              \
  for (__typeof((c).begin()) i = (c).begin(); i != (c).end(); ++i)
#define ALL(c) (c).begin(), (c).end()
const int INF = 1 << 29;

typedef double Weight;
struct Edge {
  int src, dst;
  Weight weight;
  int c; // c ÍOtÅÍ§À¬xAqueue ÅÍ¬x
  Edge(int src, int dst, Weight weight, int c)
      : src(src), dst(dst), weight(weight), c(c) {}
};

bool operator<(const Edge &e, const Edge &f) {
  return e.weight != f.weight ? e.weight > f.weight : // !!INVERSE!!
             e.src != f.src ? e.src < f.src
         : e.dst != f.dst   ? e.dst < f.dst
                            : e.c < f.c;
}

typedef vector<Edge> Edges;
typedef vector<Edges> Graph;
typedef pair<int, int> pii;

double dist[30][30][32]; // dist[i][j][k] = Xs[h k ÌóÔÅ j ©ç
                         // i ÉÂ­ÅZ£

double dijkstra(const Graph &g, int s, int t) {
  int n = g.size();
  REP(i, n) REP(j, n) REP(k, 32) dist[i][j][k] = INF;
  priority_queue<Edge> Q;
  Q.push(Edge(s, s, 0, 0));
  int cnt = 0;
  while (!Q.empty()) {
    Edge e = Q.top();
    Q.pop();
    if (e.dst == t && e.c == 1)
      break;
    REP(k, 3) {
      int v = e.c - 1 + k;
      if (v <= 0)
        continue;
      if (dist[e.dst][e.src][v] < e.weight)
        continue;
      FOR(f, g[e.dst]) {
        if (v > f->c)
          continue;
        if (f->dst == e.src)
          continue;
        double hoge = e.weight + f->weight / v;
        if (dist[f->dst][f->src][v] > hoge) {
          dist[f->dst][f->src][v] = hoge;
          Q.push(Edge(f->src, f->dst, hoge, v));
        }
      }
    }
    if (cnt++ > 200000)
      break;
  }

  double res = INF;
  REP(i, n)
  res = min(res, dist[t][i][1]);
  return res;
}

int main() {
  int n, m;
  while (cin >> n >> m, n || m) {
    int s, t;
    cin >> s >> t;
    s--;
    t--;
    Graph g(n);
    REP(i, m) {
      int x, y, d, c;
      cin >> x >> y >> d >> c;
      x--;
      y--;
      g[x].push_back(Edge(x, y, d, c));
      g[y].push_back(Edge(y, x, d, c));
    }
    double res = dijkstra(g, s, t);
    if (res == INF)
      cout << "unreachable" << endl;
    else
      printf("%.5f\n", res);
  }
}