Language: C++

#include <bits/stdc++.h>

using namespace std;
typedef long long ll;
typedef pair<ll, ll> p_ll;

template<class T>
void debug(T itr1, T itr2) { auto now = itr1; while(now<itr2) { cout << *now << " "; now++; } cout << endl; }
#define repr(i,from,to) for (int i=(int)from; i<(int)to; i++)
#define all(vec) vec.begin(), vec.end()
#define rep(i,N) repr(i,0,N)
#define per(i,N) for (int i=(int)N-1; i>=0; i--)

const ll MOD = pow(10,9)+7;
const ll LLINF = pow(2,61)-1;
const int INF = pow(2,30)-1;

vector<ll> fac;
void c_fac(int x=pow(10,6)+10) { fac.resize(x,true); rep(i,x) fac[i] = i ? (fac[i-1]*i)%MOD : 1; }
ll inv(ll a, ll m=MOD) { ll b = m, x = 1, y = 0; while (b!=0) { int d = a/b; a -= b*d; swap(a,b); x -= y*d; swap(x,y); } return (x+m)%m; }
ll nck(ll n, ll k) { return fac[n]*inv(fac[k]*fac[n-k]%MOD)%MOD; }
ll gcd(ll a, ll b) { if (a<b) swap(a,b); return b==0 ? a : gcd(b, a%b); }
ll lcm(ll a, ll b) { return a/gcd(a,b)*b; }

// ----------------------------------------------------------------------
// ----------------------------------------------------------------------

struct edge { 
  int from; int to; 
  bool operator<(const edge& x) const { return from<x.from||(from==x.from&&to<x.to); }
};
vector<vector<int>> adj;
vector<ll> num, oe;
map<edge, ll> e;
bool modify = false;

bool dfs(int n=0, int p=-1) {
  for (auto x: adj[n]) {
    if (x==p) continue;
    if (num[x]!=LLINF) {
      if (num[x]+num[n]==e[{x,n}]) continue;
      else {
        if (modify) return false;
        else {
          if ((e[{x,n}]-(num[x]+num[n]))%2) return false;
          else { 
            ll v = (e[{x,n}]-(num[x]+num[n]))/2; 
            fill(all(num),LLINF); num[x] = v;
            fill(all(oe),0); oe[x] = 1;
            modify = true;
            return dfs(x,-1);
          }
        }
      }
    }
    else {
      oe[x] = oe[n]*-1;
      num[x] = e[{x,n}] - num[n];
      if (!dfs(x,n)) return false;
    }
  }
  return true;
}

// ----------------------------------------------------------------------
// ----------------------------------------------------------------------

int main() {
  int N, M; cin >> N >> M;
  adj.resize(N);
  oe.resize(N); oe[0] = 1;
  num.resize(N,LLINF); num[0] = 0;
  rep(i,M) {
    int u, v; cin >> u >> v; u--; v--;
    ll s; cin >> s;
    adj[u].push_back(v); adj[v].push_back(u);
    e[(edge){u,v}] = s; e[(edge){v,u}] = s;
  }

  if (!dfs()) cout << 0 << endl;
  else {
    if (modify) {
      bool ok = true;
      rep(i,n) ok &= num[i]>0;
      cout << ok << endl;
    }
    else {
      ll omax = -1*LLINF, omin = LLINF;
      ll emax = -1*LLINF, emin = LLINF;
      rep(i,n) {
        if (oe[i]==1) { omax = max(omax,num[i]); omin = min(omin,num[i]); }
        else { emax = max(emax,num[i]); emin = min(emin,num[i]); }
      }
      // cout << omin << "~" << omax << " " << emin << "~" << emax << endl;
      debug(all(num));
      ll result = max((ll)0,omin+emin-1);
      cout << result << endl;
    }
  }
  return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:84:13: error: 'n' was not declared in this scope
   84 |       rep(i,n) ok &= num[i]>0;
      |             ^
a.cc:9:54: note: in definition of macro 'repr'
    9 | #define repr(i,from,to) for (int i=(int)from; i<(int)to; i++)
      |                                                      ^~
a.cc:84:7: note: in expansion of macro 'rep'
   84 |       rep(i,n) ok &= num[i]>0;
      |       ^~~
a.cc:90:13: error: 'n' was not declared in this scope
   90 |       rep(i,n) {
      |             ^
a.cc:9:54: note: in definition of macro 'repr'
    9 | #define repr(i,from,to) for (int i=(int)from; i<(int)to; i++)
      |                                                      ^~
a.cc:90:7: note: in expansion of macro 'rep'
   90 |       rep(i,n) {
      |       ^~~