Language: C++

#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <climits>
#include <cfloat>
#include <ctime>
#include <cassert>
#include <map>
#include <utility>
#include <set>
#include <iostream>
#include <memory>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <sstream>
#include <complex>
#include <stack>
#include <queue>
#include <numeric>
#include <list>
#include <iomanip>
#include <fstream>
#include <bitset>

using namespace std;

#define foreach(it, c) for (__typeof__((c).begin()) it=(c).begin(); it != (c).end(); ++it)
template <typename T> void print_container(ostream& os, const T& c) { const char* _s = " "; if (!c.empty()) { __typeof__(c.begin()) last = --c.end(); foreach (it, c) { os << *it; if (it != last) os << _s; } } }
template <typename T> ostream& operator<<(ostream& os, const vector<T>& c) { print_container(os, c); return os; }
template <typename T> ostream& operator<<(ostream& os, const set<T>& c) { print_container(os, c); return os; }
template <typename T> ostream& operator<<(ostream& os, const multiset<T>& c) { print_container(os, c); return os; }
template <typename T> ostream& operator<<(ostream& os, const deque<T>& c) { print_container(os, c); return os; }
template <typename T, typename U> ostream& operator<<(ostream& os, const map<T, U>& c) { print_container(os, c); return os; }
template <typename T, typename U> ostream& operator<<(ostream& os, const pair<T, U>& p) { os << "(" << p.first << ", " << p.second << ")"; return os; }

template <typename T> void print(T a, int n, const string& split = " ") { for (int i = 0; i < n; i++) { cout << a[i]; if (i + 1 != n) cout << split; } cout << endl; }
template <typename T> void print2d(T a, int w, int h, int width = -1, int br = 0) { for (int i = 0; i < h; ++i) { for (int j = 0; j < w; ++j) { if (width != -1) cout.width(width); cout << a[i][j] << ' '; } cout << endl; } while (br--) cout << endl; }
template <typename T> void input(T& a, int n) { for (int i = 0; i < n; ++i) cin >> a[i]; }
#define dump(v) (cerr << #v << ": " << v << endl)

#define rep(i, n) for (int i = 0; i < (int)(n); ++i)
#define erep(i, n) for (int i = 0; i <= (int)(n); ++i)
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define clr(a, x) memset(a, x, sizeof(a))
#define sz(a) ((int)(a).size())
#define mp(a, b) make_pair(a, b)
#define ten(n) ((long long)(1e##n))

template <typename T, typename U> void upmin(T& a, const U& b) { a = min<T>(a, b); }
template <typename T, typename U> void upmax(T& a, const U& b) { a = max<T>(a, b); }
template <typename T> void uniq(T& a) { sort(a.begin(), a.end()); a.erase(unique(a.begin(), a.end()), a.end()); }
template <class T> string to_s(const T& a) { ostringstream os; os << a; return os.str(); }
template <class T> T to_T(const string& s) { istringstream is(s); T res; is >> res; return res; }
void fast_io() { cin.tie(0); ios::sync_with_stdio(false); }
bool in_rect(int x, int y, int w, int h) { return 0 <= x && x < w && 0 <= y && y < h; }

typedef long long ll;
typedef pair<int, int> pint;

const int dx[] = { 0, 1, 0, -1 };
const int dy[] = { 1, 0, -1, 0 };



template <typename FLOW, typename COST>
class PrimalDual
{
private:
    struct PrimalDualEdge
    {
        int to;
        FLOW cap;
        COST cost;
        int rev;
        PrimalDualEdge(int to, FLOW cap, COST cost, int rev)
            : to(to), cap(cap), cost(cost), rev(rev) { }
    };
public:
    int V;
    vector<vector<PrimalDualEdge> > g;

    PrimalDual(int V) : V(V), g(V) { }

    void add_edge(int from, int to, FLOW cap, COST cost)
    {
        g[from].push_back(PrimalDualEdge(to, cap, cost, g[to].size()));
        g[to].push_back(PrimalDualEdge(from, 0, -cost, g[from].size() - 1));
    }
    void add_undirected(int a, int b, FLOW cap, COST cost)
    {
        add_edge(a, b, cap, cost);
        add_edge(b, a, cap, cost);
    }

    COST min_cost_flow(int s, int t, FLOW f)
    {
        vector<COST> h(V);
        COST res = 0;
        int _f = f;
        while (_f > 0)
        {
            typedef pair<COST, int> _p;
            const COST _INF = (COST)((1LL << 60) | (1 << 29));
            priority_queue<_p, vector<_p>, greater<_p> > q;
            vector<COST> dis(V, _INF);
            vector<int> prevv(V), preve(V);
            dis[s] = 0;
            q.push(_p(0, s));
            while (!q.empty())
            {
                _p p = q.top(); q.pop();
                int v = p.second;
                COST cost = p.first;
                if (cost > dis[v])
                    continue;

                for (int i = 0; i < g[v].size(); ++i)
                {
                    PrimalDualEdge& e = g[v][i];
                    const COST _eps = 1e-10;
                    COST c = cost + e.cost + h[v] - h[e.to];
                    if (e.cap > 0 && c + _eps < dis[e.to])
                    {
                        dis[e.to] = c;
                        prevv[e.to] = v;
                        preve[e.to] = i;
                        q.push(_p(c, e.to));
                    }
                }
            }

            if (dis[t] == _INF)
            {
                // cant flow _f
                return _INF;
            }

            for (int i = 0; i < V; ++i)
                h[i] += dis[i];

            FLOW d = _f;
            for (int i = t; i != s; i = prevv[i])
                d = min(d, g[prevv[i]][preve[i]].cap);
            _f -= d;
            res += d * h[t];
            for (int i = t; i != s; i = prevv[i])
            {
                PrimalDualEdge& e = g[prevv[i]][preve[i]];
                e.cap -= d;
                g[e.to][e.rev].cap += d;
            }
        }

        return res;
    }

    COST min_cost_flow_spfa(int s, int t, FLOW f)
    {
        COST res = 0;
        int _f = f;
        while (_f > 0)
        {
            typedef pair<COST, int> _p;
            const COST _INF = (COST)((1LL << 60) | (1 << 29));
            vector<COST> dis(V, _INF);
            vector<int> prevv(V), preve(V);

            vector<bool> in_q(V);
            queue<_p> q;

            dis[s] = 0;
            q.push(_p(0, s));
            in_q[s] = true;

            while (!q.empty())
            {
                _p p = q.fron(); q.pop();
                int v = p.second;
                COST cost = p.first;
                in_q[v] = false;
                if (cost > dis[v])
                    continue;

                for (int i = 0; i < g[v].size(); ++i)
                {
                    PrimalDualEdge& e = g[v][i];
                    const COST _eps = 1e-10;
                    COST c = cost + e.cost;
                    if (e.cap > 0 && c + _eps < dis[e.to])
                    {
                        dis[e.to] = c;
                        prevv[e.to] = v;
                        preve[e.to] = i;
                        if (!in_q[e.to])
                        {
                            q.push(_p(c, e.to));
                            in_q[v] = true;
                        }
                    }
                }
            }

            if (dis[t] == _INF)
            {
                // cant flow _f
                return _INF;
            }

            FLOW d = _f;
            for (int i = t; i != s; i = prevv[i])
                d = min(d, g[prevv[i]][preve[i]].cap);
            _f -= d;
            res += d * dis[t];
            for (int i = t; i != s; i = prevv[i])
            {
                PrimalDualEdge& e = g[prevv[i]][preve[i]];
                e.cap -= d;
                g[e.to][e.rev].cap += d;
            }
        }

        return res;
    }
};
int main()
{
    fast_io();

    int n, x_left, x_right;
    ll v;
    cin >> n >> v >> x_left >> x_right;

    int x[3333], t[3333], p[3333];
    rep(i, n)
        cin >> x[i] >> t[i] >> p[i];

    PrimalDual<int, ll> pd(2 * n + 2);
    int src = 0, sink = 1;
    int in = 2;
    int out = in + n;

    pd.add_edge(src, sink, 2, 0);
    rep(i, n)
    {
        pd.add_edge(in + i, out + i, 1, -p[i]);
        pd.add_edge(out + i, sink, 1, 0);

        {
            int cap = (abs(x[i] - x_left) <= v * t[i]) + (abs(x[i] - x_right) <= v * t[i]);
            if (cap)
                pd.add_edge(src, in + i, cap, 0);
        }

        rep(j, n)
        {
            if (t[i] < t[j])
            {
                if (abs(x[j] - x[i]) <= v * (t[j] - t[i]))
                    pd.add_edge(out + i, in + j, 1, 0);
            }
        }
    }

    ll mcf = pd.min_cost_flow_spfa(src, sink, 2);
    assert(mcf <= 0);
    cout << -mcf << endl;
}

Compiler output:
a.cc: In instantiation of 'COST PrimalDual<FLOW, COST>::min_cost_flow_spfa(int, int, FLOW) [with FLOW = int; COST = long long int]':
a.cc:268:35:   required from here
  268 |     ll mcf = pd.min_cost_flow_spfa(src, sink, 2);
      |              ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~
a.cc:181:26: error: 'class std::queue<std::pair<long long int, int>, std::deque<std::pair<long long int, int>, std::allocator<std::pair<long long int, int> > > >' has no member named 'fron'; did you mean 'front'?
  181 |                 _p p = q.fron(); q.pop();
      |                        ~~^~~~
      |                        front