Language: C++

#pragma GCC optimize ("O3")
#include "bits/stdc++.h"

using namespace std;
using ll = long long int;

#define debugos cout
#define debug(v) {printf("L%d %s > ",__LINE__,#v);debugos<<(v)<<endl;}
#define debugv(v) {printf("L%d %s > ",__LINE__,#v);for(auto e:(v)){debugos<<e<<" ";}debugos<<endl;}
#define debuga(m,w) {printf("L%d %s > ",__LINE__,#m);for(int x=0;x<(w);x++){debugos<<(m)[x]<<" ";}debugos<<endl;}
#define debugaa(m,h,w) {printf("L%d %s >\n",__LINE__,#m);for(int y=0;y<(h);y++){for(int x=0;x<(w);x++){debugos<<(m)[y][x]<<" ";}debugos<<endl;}}
#define ALL(v) (v).begin(),(v).end()
#define repeat(cnt,l) for(remove_reference<remove_const<decltype(l)>::type>::type cnt=0;(cnt)<(l);++(cnt))
#define rrepeat(cnt,l) for(auto cnt=(l)-1;0<=(cnt);--(cnt))
#define iterate(cnt,b,e) for(auto cnt=(b);(cnt)!=(e);++(cnt))
#define diterate(cnt,b,e) for(auto cnt=(b);(cnt)!=(e);--(cnt))
const ll MD = 1000000007ll; const long double PI = 3.1415926535897932384626433832795L;
inline void assert_call(bool assertion, function<void()> f) { if (!assertion) { cerr << "assertion fault:" << endl; f(); abort(); } }
template<typename T1, typename T2> inline ostream& operator <<(ostream &o, const pair<T1, T2> p) { o << '(' << p.first << ':' << p.second << ')'; return o; }
template<typename Vec> inline ostream& _ostream_vecprint(ostream& os, const Vec& a) {
    os << '['; for (const auto& e : a) os << ' ' << e << ' '; os << ']'; return os;
}
template<typename T> inline ostream& operator<<(ostream& o, const vector<T>& v) { return _ostream_vecprint(o, v); }
template<typename T, size_t S> inline ostream& operator<<(ostream& o, const array<T, S>& v) { return _ostream_vecprint(o, v); }
template<typename T> inline T& maxset(T& to, const T& val) { return to = max(to, val); }
template<typename T> inline T& minset(T& to, const T& val) { return to = min(to, val); }
void bye(string s, int code = 0) { cout << s << endl; exit(code); }
mt19937_64 randdev(8901016);
template<typename T> inline T rand(T l, T h) { return uniform_int_distribution<T>(l, h)(randdev); }
template<> inline double rand<double>(double l, double h) { return uniform_real_distribution<double>(l, h)(randdev); }
template<> inline float rand<float>(float l, float h) { return uniform_real_distribution<float>(l, h)(randdev); }

#if defined(_WIN32) || defined(_WIN64)
#define getchar_unlocked _getchar_nolock
#define putchar_unlocked _putchar_nolock
#elif defined(__GNUC__)
#else
#define getchar_unlocked getchar
#define putchar_unlocked putchar
#endif
namespace {
#define isvisiblechar(c) (0x21<=(c)&&(c)<=0x7E)
    class MaiScanner {
    public:
        template<typename T> void input_integer(T& var) {
            var = 0; T sign = 1;
            int cc = getchar_unlocked();
            for (; cc<'0' || '9'<cc; cc = getchar_unlocked())
                if (cc == '-') sign = -1;
            for (; '0' <= cc && cc <= '9'; cc = getchar_unlocked())
                var = (var << 3) + (var << 1) + cc - '0';
            var = var * sign;
        }
        inline int c() { return getchar_unlocked(); }
        inline MaiScanner& operator>>(int& var) { input_integer<int>(var); return *this; }
        inline MaiScanner& operator>>(long long& var) { input_integer<long long>(var); return *this; }
        inline MaiScanner& operator>>(string& var) {
            int cc = getchar_unlocked();
            for (; !isvisiblechar(cc); cc = getchar_unlocked());
            for (; isvisiblechar(cc); cc = getchar_unlocked())
                var.push_back(cc);
            return *this;
        }
        template<typename IT> void in(IT begin, IT end) { for (auto it = begin; it != end; ++it) *this >> *it; }
    };
    class MaiPrinter {
    public:
        template<typename T>
        void output_integer(T var) {
            if (var == 0) { putchar_unlocked('0'); return; }
            if (var < 0)
                putchar_unlocked('-'),
                var = -var;
            char stack[32]; int stack_p = 0;
            while (var)
                stack[stack_p++] = '0' + (var % 10),
                var /= 10;
            while (stack_p)
                putchar_unlocked(stack[--stack_p]);
        }
        inline MaiPrinter& operator<<(char c) { putchar_unlocked(c); return *this; }
        inline MaiPrinter& operator<<(int var) { output_integer<int>(var); return *this; }
        inline MaiPrinter& operator<<(long long var) { output_integer<long long>(var); return *this; }
        inline MaiPrinter& operator<<(char* str_p) { while (*str_p) putchar_unlocked(*(str_p++)); return *this; }
        inline MaiPrinter& operator<<(const string& str) {
            const char* p = str.c_str();
            const char* l = p + str.size();
            while (p < l) putchar_unlocked(*p++);
            return *this;
        }
        template<typename IT> void join(IT begin, IT end, char sep = ' ') { for (bool b = 0; begin != end; ++begin, b = 1) b ? *this << sep << *begin : *this << *begin; }
    };
}
MaiScanner scanner;
MaiPrinter printer;



// Edge構造体を定義する無向グラフ

class GraphE {
public:
    typedef int W_T;
    struct Edge {
        int u, v;
        W_T value;
        Edge(int from = 0, int to = 0, W_T value = 0) :u(from), v(to), value(value) {}
        inline int to(int _v) const { return _v == v ? u : v; }
    };
    size_t n;
    vector<vector<int>> vertex_to;
    vector<Edge> edges;

    GraphE(int n = 1) :n(n), vertex_to(n) { }

    void resize(size_t _n) {
        n = _n;
        vertex_to.resize(_n);
    }
    void connect(int from, int to, W_T val = 0) {
        vertex_to[(size_t)from].push_back((int)edges.size());
        vertex_to[(size_t)to].push_back((int)edges.size());
        edges.emplace_back(from, to, val);
    }
};



int N, M;
GraphE graph;


template<typename T> inline T limit(T val, T low, T high) {return val < low ? low : val > high ? high : val; }

vector<int> visited;
vector<pair<ll, ll>> lh;

pair<ll, ll> dfs(int idx = 0, ll low = 1, ll high = 1e9, int flip = 1) {
    
    //cout << idx << make_pair(low, high) << endl;
    
    if (-1*flip == visited[idx]){
        if (low%2 == lh[idx].second%2){
            ll t = (low + lh[idx].second) / 2;
            if (t > high || t < lh[idx].first) bye("0");
            low = high = t;
        }
        else if (high%2 == lh[idx].first%2){
            low = high = (high + lh[idx].first) / 2;
            if (t > lh[idx].second || t < low) bye("0");
            low = high = t;
        }
        else{
            bye("0");
        }
    }

    maxset(lh[idx].first, low); low = lh[idx].first;
    minset(lh[idx].second, high); high = lh[idx].second;

    if (low > high || low < 1 || high < 1) bye("0");

    if (visited[idx]) {
        return make_pair(low, high);
    }
    visited[idx] = flip;

    for (int ei : graph.vertex_to[idx]) {
        auto edge = graph.edges[ei];
        int to = edge.to(idx);
        ll s = edge.value;

        ll l2 = s - high;
        ll h2 = s - low;
        maxset(l2, 1ll);
        maxset(h2, 1ll);
        auto p = dfs(to, l2, h2, -flip);
        l2 = p.first;
        h2 = p.second;
        high = s - l2;
        low = s - h2;

        maxset(lh[idx].first, low); low = lh[idx].first;
        minset(lh[idx].second, high); high = lh[idx].second;
        if (low > high || low < 1 || high < 1) bye("0");
    }
    
    return make_pair(low, high);
}


int main() {

    scanner >> N >> M;
    graph.resize(N);
    graph.edges.reserve(M);

    visited.resize(N);
    lh.resize(N, pair<ll,ll>(1, 1e9));

    repeat(i, M) {
        ll u, v, s;
        scanner >> u >> v >> s;
        --u; --v;
        graph.connect(u, v, s);
    }

    auto p = dfs();


    cout << (p.second - p.first + 1) << endl;



    return 0;
}

Compiler output:
a.cc: In function 'std::pair<long long int, long long int> dfs(int, ll, ll, int)':
a.cc:150:17: error: 't' was not declared in this scope; did you mean 'tm'?
  150 |             if (t > lh[idx].second || t < low) bye("0");
      |                 ^
      |                 tm
a.cc:151:26: error: 't' was not declared in this scope; did you mean 'tm'?
  151 |             low = high = t;
      |                          ^
      |                          tm