Problem p03306 (C++)

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

#include <algorithm>
#include <iostream>

#include <array>
#include <bitset>
#include <complex>
#include <cstring>
#include <deque>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <valarray>
#include <vector>

#include <cassert>
#include <chrono>
#include <cmath>
#include <functional>
#include <iomanip>
#include <numeric>
#include <random>

#include <memory>

using namespace std;
#define int long long

typedef long long ll;
typedef unsigned long long ull;
// typedef unsigned __int128 HASH;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<ull, ull> pullull;
typedef pair<ll, int> plli;
typedef pair<double, int> pdi;
typedef pair<long double, int> pdbi;
typedef pair<int, pii> pipii;
typedef pair<ll, pll> plpll;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<vi> vvi;
typedef vector<vvi> vvvi;
typedef vector<pii> vpii;
typedef vector<vector<int>> mat;

#define rep(i, n) for (int i = 0; i < (n); i++)
#define rep2(i, a, b) for (int i = (a); i < (b); i++)
#define rrep(i, n) for (int i = (n); i > 0; i--)
#define rrep2(i, a, b) for (int i = (a); i > b; i--)
#define pb push_back
#define fi first
#define se second
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()

const ll hmod1 = 999999937;
const ll hmod2 = 1000000000 + 9;
const int INF = 1 << 30;
const ll INFLL = 1LL << 62;
const long double EPS = 1e-12;
const ll mod = 1000000000 + 7;
// const ll mod = 998244353;
const int dx4[4] = {1, 0, -1, 0};
const int dy4[4] = {0, 1, 0, -1};
const int dx8[8] = {1, 1, 1, 0, 0, -1, -1, -1};
const int dy8[8] = {0, 1, -1, 1, -1, 0, 1, -1};
const long double pi = 3.141592653589793;

#define addm(X, Y) (X) = ((X) + ((Y) % mod) + mod) % mod
#define inside(y, x, h, w)                                                     \
  (0 <= (y) && (y) < (h) && 0 <= (x) && (x) < (w)) ? true : false

// debug
#define DEBUG

#define DUMPOUT cout

#ifdef DEBUG
#define dump(...)                                                              \
  DUMPOUT << #__VA_ARGS__ << " :[" << __FUNCTION__ << ":" << __LINE__ << "]"   \
          << endl;                                                             \
  DUMPOUT << "    ";                                                           \
  dump_func(__VA_ARGS__)
#else
#define dump(...)
#endif

void dump_func() { DUMPOUT << endl; };

template <class Head, class... Tail>
void dump_func(Head &&head, Tail &&...tail) {
  DUMPOUT << head;
  if (sizeof...(Tail) == 0)
    DUMPOUT << " ";
  else
    DUMPOUT << ", ";
  dump_func(std::move(tail)...);
}

// ostream
template <typename T> ostream &operator<<(ostream &os, vector<T> &vec) {
  os << "[";
  for (int i = 0; i < vec.size(); i++)
    os << vec[i] << (i + 1 == vec.size() ? "" : ", ");
  os << "]";
  return os;
}

template <typename T, typename U>
ostream &operator<<(ostream &os, pair<T, U> &pair_var) {
  os << "(" << pair_var.first << ", " << pair_var.second << ")";
  return os;
}

template <typename T, typename U>
ostream &operator<<(ostream &os, map<T, U> &map_var) {
  os << "[";
  for (auto itr = map_var.begin(); itr != map_var.end(); itr++) {
    os << "(" << itr->first << ", " << itr->second << ")";
    itr++;
    if (itr != map_var.end())
      os << ", ";
    itr--;
  }
  os << "]";
  return os;
}

template <typename T> ostream &operator<<(ostream &os, set<T> &set_var) {
  os << "[";
  for (auto itr = set_var.begin(); itr != set_var.end(); itr++) {
    os << *itr;
    ++itr;
    if (itr != set_var.end())
      os << ", ";
    itr--;
  }
  os << "]";
  return os;
}

int n, m;
vector<vector<pii>> g(100000 + 5);
vector<pii> node(100000 + 5);
vector<bool> visited(100000 + 5);
vector<int> val(100000 + 5);
int fixed_val = -1;

void dfs(int now, int par, int dist, int w) {
  visited[now] = true;
  if (dist % 2 == 0) {
    if (par != -1)
      node[now].fi = w - node[par].fi;
    else
      node[now].fi = 0;
    node[now].se = 1;
  } else {
    node[now].fi = w - node[par].fi;
    node[now].se = -1;
  }
  for (auto p : g[now]) {
    int nx = p.fi;
    if (nx == par)
      continue;
    int c = p.se;
    if (visited[nx]) {
      int co = node[now].se + node[nx].se;
      if (co == 0 && node[now].fi + node[nx].fi != c) {
        cerr << "co is " << 0 << endl;
        cout << 0 << endl;
        exit(0);
      } else if (co == 0) {
        continue;
      }
      // node[nx].fi + node[now].fi + cox = c;
      // x = (c - node[nx].fi - node[now].fi) / co;
      if ((c - node[nx].fi - node[now].fi) % abs(co) != 0) {
        cerr << "not divide " << c - node[nx].fi - node[now].fi << " " << co
             << endl;
        cout << 0 << endl;
        exit(0);
      }
      int num = (c - node[nx].fi - node[now].fi) / co;
      if (num <= 0) {
        cout << 0 << endl;
        exit(0);
      }
      fixed_val = num;
      return;
    }
    dfs(nx, now, dist + 1, c);
    if (fixed_val != -1)
      return;
  }
  return;
}

void dfs2(int now, int par) {
  visited[now] = true;
  for (auto p : g[now]) {
    int nx = p.fi;
    int c = p.se;
    if (nx == par || visited[nx])
      continue;
    val[nx] = c - val[now];
    dfs2(nx, now);
  }
}

signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cin >> n >> m;
  rep(i, m) {
    int u, v, s;
    cin >> u >> v >> s;
    u--;
    v--;
    g[u].push_back({v, s});
    g[v].push_back({u, s});
  }
  dfs(0, -1, 0, 0);
  rep(i, n) visited[i] = false;
  if (fixed_val > 0) {
    cerr << fixed_val << endl;
    val[0] = fixed_val;
    dfs2(0, -1);
    bool ok = true;
    rep(i, n) {
      for (auto p : g[i]) {
        int j = p.fi;
        int c = p.se;
        cerr << c << " " << val[i] << " " << val[j] << endl;
        if (c != val[i] + val[j] || val[i] <= 0 || val[j] <= 0) {
          ok = false;
          break;
        }
      }
      if (!ok)
        break;
    }
    if (ok)
      cout << 1 << endl;
    else
      cout << 0 << endl;
    return 0;
  }
  assert(m == n - 1);
  cerr << "Tree" << endl;
  int mn = 1;
  int mx = INF;
  rep(i, n) {
    // 1 <= a + node[i].se*x <= min(g[i].edge_cost)
    int mnc = INF;
    rep(j, g[i].size()) { mnc = min(mnc, g[i][j].se); }
    int a = node[i].fi;
    if (node[i].se > 0) {
      mn = max(mn, 1 - a);
      mx = min(mx, mnc - a);
    } else {
      mn = max(mn, -(mnc - a));
      mx = min(mx, -(1 - a));
    }
  }
  cerr << mx << " " << mn << endl;
  cout << max(0LL, mx - mn + 1) << endl;
}


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

#include <algorithm>
#include <iostream>

#include <array>
#include <bitset>
#include <complex>
#include <cstring>
#include <deque>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <valarray>
#include <vector>

#include <cassert>
#include <chrono>
#include <cmath>
#include <functional>
#include <iomanip>
#include <numeric>
#include <random>

#include <memory>

using namespace std;
#define int long long

typedef long long ll;
typedef unsigned long long ull;
// typedef unsigned __int128 HASH;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<ull, ull> pullull;
typedef pair<ll, int> plli;
typedef pair<double, int> pdi;
typedef pair<long double, int> pdbi;
typedef pair<int, pii> pipii;
typedef pair<ll, pll> plpll;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<vi> vvi;
typedef vector<vvi> vvvi;
typedef vector<pii> vpii;
typedef vector<vector<int>> mat;

#define rep(i, n) for (int i = 0; i < (n); i++)
#define rep2(i, a, b) for (int i = (a); i < (b); i++)
#define rrep(i, n) for (int i = (n); i > 0; i--)
#define rrep2(i, a, b) for (int i = (a); i > b; i--)
#define pb push_back
#define fi first
#define se second
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()

const ll hmod1 = 999999937;
const ll hmod2 = 1000000000 + 9;
const int INF = 1 << 30;
const ll INFLL = 1LL << 62;
const long double EPS = 1e-12;
const ll mod = 1000000000 + 7;
// const ll mod = 998244353;
const int dx4[4] = {1, 0, -1, 0};
const int dy4[4] = {0, 1, 0, -1};
const int dx8[8] = {1, 1, 1, 0, 0, -1, -1, -1};
const int dy8[8] = {0, 1, -1, 1, -1, 0, 1, -1};
const long double pi = 3.141592653589793;

#define addm(X, Y) (X) = ((X) + ((Y) % mod) + mod) % mod
#define inside(y, x, h, w)                                                     \
  (0 <= (y) && (y) < (h) && 0 <= (x) && (x) < (w)) ? true : false

// debug
#define DEBUG

#define DUMPOUT cout

#ifdef DEBUG
#define dump(...)                                                              \
  DUMPOUT << #__VA_ARGS__ << " :[" << __FUNCTION__ << ":" << __LINE__ << "]"   \
          << endl;                                                             \
  DUMPOUT << "    ";                                                           \
  dump_func(__VA_ARGS__)
#else
#define dump(...)
#endif

void dump_func() { DUMPOUT << endl; };

template <class Head, class... Tail>
void dump_func(Head &&head, Tail &&...tail) {
  DUMPOUT << head;
  if (sizeof...(Tail) == 0)
    DUMPOUT << " ";
  else
    DUMPOUT << ", ";
  dump_func(std::move(tail)...);
}

// ostream
template <typename T> ostream &operator<<(ostream &os, vector<T> &vec) {
  os << "[";
  for (int i = 0; i < vec.size(); i++)
    os << vec[i] << (i + 1 == vec.size() ? "" : ", ");
  os << "]";
  return os;
}

template <typename T, typename U>
ostream &operator<<(ostream &os, pair<T, U> &pair_var) {
  os << "(" << pair_var.first << ", " << pair_var.second << ")";
  return os;
}

template <typename T, typename U>
ostream &operator<<(ostream &os, map<T, U> &map_var) {
  os << "[";
  for (auto itr = map_var.begin(); itr != map_var.end(); itr++) {
    os << "(" << itr->first << ", " << itr->second << ")";
    itr++;
    if (itr != map_var.end())
      os << ", ";
    itr--;
  }
  os << "]";
  return os;
}

template <typename T> ostream &operator<<(ostream &os, set<T> &set_var) {
  os << "[";
  for (auto itr = set_var.begin(); itr != set_var.end(); itr++) {
    os << *itr;
    ++itr;
    if (itr != set_var.end())
      os << ", ";
    itr--;
  }
  os << "]";
  return os;
}

int n, m;
vector<vector<pii>> g(100000 + 5);
vector<pii> node(100000 + 5);
vector<bool> visited(100000 + 5);
vector<int> val(100000 + 5);
int fixed_val = -1;

void dfs(int now, int par, int dist, int w) {
  visited[now] = true;
  if (dist % 2 == 0) {
    if (par != -1)
      node[now].fi = w - node[par].fi;
    else
      node[now].fi = 0;
    node[now].se = 1;
  } else {
    node[now].fi = w - node[par].fi;
    node[now].se = -1;
  }
  for (auto p : g[now]) {
    int nx = p.fi;
    if (nx == par)
      continue;
    int c = p.se;
    if (visited[nx]) {
      int co = node[now].se + node[nx].se;
      if (co == 0 && node[now].fi + node[nx].fi != c) {
        cerr << "co is " << 0 << endl;
        cout << 0 << endl;
        exit(0);
      } else if (co == 0) {
        continue;
      }
      // node[nx].fi + node[now].fi + cox = c;
      // x = (c - node[nx].fi - node[now].fi) / co;
      if ((c - node[nx].fi - node[now].fi) % abs(co) != 0) {
        cerr << "not divide " << c - node[nx].fi - node[now].fi << " " << co
             << endl;
        cout << 0 << endl;
        exit(0);
      }
      int num = (c - node[nx].fi - node[now].fi) / co;
      if (num <= 0) {
        cout << 0 << endl;
        exit(0);
      }
      fixed_val = num;
      return;
    }
    dfs(nx, now, dist + 1, c);
    if (fixed_val != -1)
      return;
  }
  return;
}

void dfs2(int now, int par) {
  visited[now] = true;
  for (auto p : g[now]) {
    int nx = p.fi;
    int c = p.se;
    if (nx == par || visited[nx])
      continue;
    val[nx] = c - val[now];
    dfs2(nx, now);
  }
}

signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cin >> n >> m;
  rep(i, m) {
    int u, v, s;
    cin >> u >> v >> s;
    u--;
    v--;
    g[u].push_back({v, s});
    g[v].push_back({u, s});
  }
  dfs(0, -1, 0, 0);
  rep(i, n) visited[i] = false;
  if (fixed_val > 0) {
    cerr << fixed_val << endl;
    val[0] = fixed_val;
    dfs2(0, -1);
    bool ok = true;
    rep(i, n) {
      for (auto p : g[i]) {
        int j = p.fi;
        int c = p.se;
        cerr << c << " " << val[i] << " " << val[j] << endl;
        if (c != val[i] + val[j] || val[i] <= 0 || val[j] <= 0) {
          ok = false;
          break;
        }
      }
      if (!ok)
        break;
    }
    if (ok)
      cout << 1 << endl;
    else
      cout << 0 << endl;
    return 0;
  }
  int mn = 1;
  int mx = INF;
  rep(i, n) {
    // 1 <= a + node[i].se*x <= min(g[i].edge_cost)
    int mnc = INF;
    rep(j, g[i].size()) { mnc = min(mnc, g[i][j].se); }
    int a = node[i].fi;
    if (node[i].se > 0) {
      mn = max(mn, 1 - a);
      mx = min(mx, mnc - a);
    } else {
      mn = max(mn, -(mnc - a));
      mx = min(mx, -(1 - a));
    }
  }
  cerr << mx << " " << mn << endl;
  cout << max(0LL, mx - mn + 1) << endl;
}