Problem p02868 (C++)

Buggy submission (status: Time Limit Exceeded):
#define DEBUG 0
#include <algorithm>
#include <cassert>
#include <cmath>
#include <cstring>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <utility>
#include <vector>
using namespace std;
using ll = long long;
using ull = unsigned long long;
using ld = long double;
using vll = vector<ll>;
using vvll = vector<vll>;
using pll = pair<ll, ll>;
using vpll = vector<pll>;
using vvpll = vector<vpll>;
using tll = tuple<ll, ll, ll>;
using vtll = vector<tll>;
using vvtll = vector<vtll>;
#define all(v) (v).begin(), (v).end()
#define for1(i, n) for (ll i = 0; i < (n); i++)
#define for2(i, m, n) for (ll i = (m); i < (n); i++)
#define for3(i, m, n, d) for (ll i = (m); i < (n); i += (d))
#define rfor2(i, m, n) for (ll i = (m); i > (n); i--)
#define rfor3(i, m, n, d) for (ll i = (m); i > (n); i += (d))
#define PI 3.1415926535897932384626433832795028841971693993751
#define INF 1111111111111111111LL
#define print(...) print_1(__VA_ARGS__)
#define in(...) in_1(__VA_ARGS__)
#if DEBUG
#define dump(...) dump_1(#__VA_ARGS__, __VA_ARGS__)
#define dumpa(...) dumpa_1(#__VA_ARGS__, __VA_ARGS__)
#else
#define dump(...)
#define dumpa(...)
#endif
template <typename Head> void dump_1(const char *str, Head &&h) {
  cerr << str << ": " << h << '\n';
}
template <typename Head, typename... Tail>
void dump_1(const char *str, Head &&h, Tail &&...t) {
  while (*str != ',') {
    cerr << *str++;
  }
  cerr << ": " << h << ' ';
  dump_1(str + 1, t...);
}
template <typename T>
void dumpa_1(const char *str, const T v[], const ll size) {
  while (*str != ',') {
    cerr << *str++;
  }
  cerr << ": ";
  for1(i, size) {
    if (i != 0) {
      cerr << ' ';
    }
    cerr << v[i];
  }
  cerr << '\n';
}
template <typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &v) {
  os << v.first << ' ' << v.second;
  return os;
}
template <typename T1, typename T2, typename T3>
ostream &operator<<(ostream &os, const tuple<T1, T2, T3> &v) {
  os << get<0>(v) << ' ' << get<1>(v) << ' ' << get<2>(v);
  return os;
}
template <typename T> ostream &operator<<(ostream &os, const vector<T> &v) {
  for (auto it = v.begin(); it != v.end(); it++) {
    if (it != v.begin()) {
      os << ' ';
    }
    os << *it;
  }
  return os;
}
template <typename T> ostream &operator<<(ostream &os, const set<T> &v) {
  for (auto it = v.begin(); it != v.end(); it++) {
    if (it != v.begin()) {
      os << ' ';
    }
    os << *it;
  }
  return os;
}
template <typename T> ostream &operator<<(ostream &os, const multiset<T> &v) {
  for (auto it = v.begin(); it != v.end(); it++) {
    if (it != v.begin()) {
      os << ' ';
    }
    os << *it;
  }
  return os;
}
template <typename T1, typename T2>
ostream &operator<<(ostream &os, const map<T1, T2> &v) {
  os << '{';
  for (auto it = v.begin(); it != v.end(); it++) {
    if (it != v.begin()) {
      os << ", ";
    }
    os << it->first << ':' << it->second;
  }
  os << '}';
  return os;
}
void Yes(void) { cout << "Yes\n"; }
void No(void) { cout << "No\n"; }
void YES(void) { cout << "YES\n"; }
void NO(void) { cout << "NO\n"; }
template <typename T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T> bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T> void vin(vector<T> &v, ll len) {
  for1(i, len) { cin >> v[i]; }
}
template <typename Head> void in_1(Head &h) { cin >> h; }
template <typename Head, typename... Tail> void in_1(Head &h, Tail &...t) {
  cin >> h;
  in_1(t...);
}
template <typename Head> void print_1(Head &&h) { cout << h << '\n'; }
template <typename Head, typename... Tail> void print_1(Head &&h, Tail &&...t) {
  cout << h << ' ';
  print_1(t...);
}
//---------------------------------------------------------
void solve() {
  ll N, M;
  in(N, M);
  vll L(M);
  vll R(M);
  vll C(M);
  vector<vector<pll>> to(N);
  for1(i, M) {
    ll l, r, c;
    in(l, r, c);
    --l;
    --r;
    to[l].emplace_back(r, c);
  }
  for2(i, 1, N) { to[i].emplace_back(i - 1, 0); }
  vll dis(N, INF);
  priority_queue<pair<ll, ll>> q;
  q.push(make_pair(0, 0));
  while (!q.empty()) {
    ll cost, loc;
    tie(cost, loc) = q.top();
    q.pop();
    cost = -cost;
    if (dis[loc] < cost) {
      continue;
    }
    dis[loc] = cost;
    for (auto t : to[loc]) {
      ll cost2 = cost + t.second;
      ll loc2 = t.first;
      q.push(make_pair(-cost2, loc2));
    }
  }
  dump(dis);
  if (dis[N - 1] == INF) {
    print(-1);
  } else {
    print(dis[N - 1]);
  }
}
//---------------------------------------------------------
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout << fixed << setprecision(16);
  cerr << fixed << setprecision(16);
  solve();
}


Fixed submission:
#define DEBUG 0
#include <algorithm>
#include <cassert>
#include <cmath>
#include <cstring>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <utility>
#include <vector>
using namespace std;
using ll = long long;
using ull = unsigned long long;
using ld = long double;
using vll = vector<ll>;
using vvll = vector<vll>;
using pll = pair<ll, ll>;
using vpll = vector<pll>;
using vvpll = vector<vpll>;
using tll = tuple<ll, ll, ll>;
using vtll = vector<tll>;
using vvtll = vector<vtll>;
#define all(v) (v).begin(), (v).end()
#define for1(i, n) for (ll i = 0; i < (n); i++)
#define for2(i, m, n) for (ll i = (m); i < (n); i++)
#define for3(i, m, n, d) for (ll i = (m); i < (n); i += (d))
#define rfor2(i, m, n) for (ll i = (m); i > (n); i--)
#define rfor3(i, m, n, d) for (ll i = (m); i > (n); i += (d))
#define PI 3.1415926535897932384626433832795028841971693993751
#define INF 1111111111111111111LL
#define print(...) print_1(__VA_ARGS__)
#define in(...) in_1(__VA_ARGS__)
#if DEBUG
#define dump(...) dump_1(#__VA_ARGS__, __VA_ARGS__)
#define dumpa(...) dumpa_1(#__VA_ARGS__, __VA_ARGS__)
#else
#define dump(...)
#define dumpa(...)
#endif
template <typename Head> void dump_1(const char *str, Head &&h) {
  cerr << str << ": " << h << '\n';
}
template <typename Head, typename... Tail>
void dump_1(const char *str, Head &&h, Tail &&...t) {
  while (*str != ',') {
    cerr << *str++;
  }
  cerr << ": " << h << ' ';
  dump_1(str + 1, t...);
}
template <typename T>
void dumpa_1(const char *str, const T v[], const ll size) {
  while (*str != ',') {
    cerr << *str++;
  }
  cerr << ": ";
  for1(i, size) {
    if (i != 0) {
      cerr << ' ';
    }
    cerr << v[i];
  }
  cerr << '\n';
}
template <typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &v) {
  os << v.first << ' ' << v.second;
  return os;
}
template <typename T1, typename T2, typename T3>
ostream &operator<<(ostream &os, const tuple<T1, T2, T3> &v) {
  os << get<0>(v) << ' ' << get<1>(v) << ' ' << get<2>(v);
  return os;
}
template <typename T> ostream &operator<<(ostream &os, const vector<T> &v) {
  for (auto it = v.begin(); it != v.end(); it++) {
    if (it != v.begin()) {
      os << ' ';
    }
    os << *it;
  }
  return os;
}
template <typename T> ostream &operator<<(ostream &os, const set<T> &v) {
  for (auto it = v.begin(); it != v.end(); it++) {
    if (it != v.begin()) {
      os << ' ';
    }
    os << *it;
  }
  return os;
}
template <typename T> ostream &operator<<(ostream &os, const multiset<T> &v) {
  for (auto it = v.begin(); it != v.end(); it++) {
    if (it != v.begin()) {
      os << ' ';
    }
    os << *it;
  }
  return os;
}
template <typename T1, typename T2>
ostream &operator<<(ostream &os, const map<T1, T2> &v) {
  os << '{';
  for (auto it = v.begin(); it != v.end(); it++) {
    if (it != v.begin()) {
      os << ", ";
    }
    os << it->first << ':' << it->second;
  }
  os << '}';
  return os;
}
void Yes(void) { cout << "Yes\n"; }
void No(void) { cout << "No\n"; }
void YES(void) { cout << "YES\n"; }
void NO(void) { cout << "NO\n"; }
template <typename T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T> bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T> void vin(vector<T> &v, ll len) {
  for1(i, len) { cin >> v[i]; }
}
template <typename Head> void in_1(Head &h) { cin >> h; }
template <typename Head, typename... Tail> void in_1(Head &h, Tail &...t) {
  cin >> h;
  in_1(t...);
}
template <typename Head> void print_1(Head &&h) { cout << h << '\n'; }
template <typename Head, typename... Tail> void print_1(Head &&h, Tail &&...t) {
  cout << h << ' ';
  print_1(t...);
}
//---------------------------------------------------------
void solve() {
  ll N, M;
  in(N, M);
  vll L(M);
  vll R(M);
  vll C(M);
  vector<vector<pll>> to(N);
  for1(i, M) {
    ll l, r, c;
    in(l, r, c);
    --l;
    --r;
    to[l].emplace_back(r, c);
  }
  for2(i, 1, N) { to[i].emplace_back(i - 1, 0); }
  vll dis(N, INF);
  priority_queue<pair<ll, ll>> q;
  q.push(make_pair(0, 0));
  while (!q.empty()) {
    ll cost, loc;
    tie(cost, loc) = q.top();
    q.pop();
    cost = -cost;
    if (dis[loc] <= cost) {
      continue;
    }
    dis[loc] = cost;
    for (auto t : to[loc]) {
      ll cost2 = cost + t.second;
      ll loc2 = t.first;
      q.push(make_pair(-cost2, loc2));
    }
  }
  dump(dis);
  if (dis[N - 1] == INF) {
    print(-1);
  } else {
    print(dis[N - 1]);
  }
}
//---------------------------------------------------------
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout << fixed << setprecision(16);
  cerr << fixed << setprecision(16);
  solve();
}