Problem p00539 (C++)

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

using namespace std;

#define MAX 1010
#define INF LLONG_MAX / 4
typedef long long ll;

struct State {
  ll v, cost;

  State(ll v, ll cost) : v(v), cost(cost) {}

  bool operator>(const State &s) const { return cost > s.cost; }
};

struct P {
  ll idx, cost;
  P(ll idx, ll cost) : idx(idx), cost(cost) {}
  bool operator<(const P &p) const { return cost < p.cost; }
};

struct Edge {
  ll to, cost;

  Edge(ll to, ll cost) : to(to), cost(cost) {}
};

ll N, M, d[MAX];
vector<Edge> G[MAX];

void dijkstra() {
  fill(d, d + N, INF);
  d[0] = 0;
  priority_queue<State, vector<State>, greater<State>> Q;
  Q.push(State(0, 0));
  while (!Q.empty()) {
    State s = Q.top();
    Q.pop();
    ll v = s.v;
    if (d[v] < s.cost) {
      continue;
    }
    for (int i = 0; i < (int)G[v].size(); i++) {
      Edge e = G[v][i];
      if (d[v] + e.cost < d[e.to]) {
        d[e.to] = d[v] + e.cost;
        Q.push(State(e.to, d[e.to]));
      }
    }
  }
}

int main() {
  ll C, a, b, c, sum = 0;
  cin >> N >> M >> C;
  for (int i = 0; i < M; i++) {
    cin >> a >> b >> c;
    a--;
    b--;
    G[a].push_back(Edge(b, c));
    G[b].push_back(Edge(a, c));
    sum += c;
  }
  dijkstra();
  vector<P> v;
  for (int i = 0; i < N; i++) {
    v.push_back(P(i, d[i]));
  }
  sort(v.begin(), v.end());
  ll res = INF, dist = 0;
  set<ll> st;
  for (int i = 0; i < N; i++) {
    ll idx = v[i].idx;
    for (int j = 0; j < (int)G[idx].size(); j++) {
      if (st.find(G[idx][j].to) != st.end()) {
        dist += G[idx][j].cost;
      }
    }
    st.insert(idx);
    res = min(res, sum - dist + v[i].cost * C);
  }
  cout << res << endl;
  return 0;
}

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

using namespace std;

#define MAX 100010
#define INF LLONG_MAX / 4
typedef long long ll;

struct State {
  ll v, cost;

  State(ll v, ll cost) : v(v), cost(cost) {}

  bool operator>(const State &s) const { return cost > s.cost; }
};

struct P {
  ll idx, cost;
  P(ll idx, ll cost) : idx(idx), cost(cost) {}
  bool operator<(const P &p) const { return cost < p.cost; }
};

struct Edge {
  ll to, cost;

  Edge(ll to, ll cost) : to(to), cost(cost) {}
};

ll N, M, d[MAX];
vector<Edge> G[MAX];

void dijkstra() {
  fill(d, d + N, INF);
  d[0] = 0;
  priority_queue<State, vector<State>, greater<State>> Q;
  Q.push(State(0, 0));
  while (!Q.empty()) {
    State s = Q.top();
    Q.pop();
    ll v = s.v;
    if (d[v] < s.cost) {
      continue;
    }
    for (int i = 0; i < (int)G[v].size(); i++) {
      Edge e = G[v][i];
      if (d[v] + e.cost < d[e.to]) {
        d[e.to] = d[v] + e.cost;
        Q.push(State(e.to, d[e.to]));
      }
    }
  }
}

int main() {
  ll C, a, b, c, sum = 0;
  cin >> N >> M >> C;
  for (int i = 0; i < M; i++) {
    cin >> a >> b >> c;
    a--;
    b--;
    G[a].push_back(Edge(b, c));
    G[b].push_back(Edge(a, c));
    sum += c;
  }
  dijkstra();
  vector<P> v;
  for (int i = 0; i < N; i++) {
    v.push_back(P(i, d[i]));
  }
  sort(v.begin(), v.end());
  ll res = INF, dist = 0;
  set<ll> st;
  for (int i = 0; i < N; i++) {
    ll idx = v[i].idx;
    for (int j = 0; j < (int)G[idx].size(); j++) {
      if (st.find(G[idx][j].to) != st.end()) {
        dist += G[idx][j].cost;
      }
    }
    st.insert(idx);
    res = min(res, sum - dist + v[i].cost * C);
  }
  cout << res << endl;
  return 0;
}