差分约束模板

洛谷模板测试七倍经验：
https://www.luogu.com.cn/record/238785118
https://www.luogu.com.cn/record/238783283
https://www.luogu.com.cn/record/238788990
https://www.luogu.com.cn/record/238791631
https://www.luogu.com.cn/record/238792334
https://www.luogu.com.cn/record/238792639
https://www.luogu.com.cn/record/238794596

struct DiffConstraints {
    int n;
    std::vector<std::vector<std::array<int, 2>>> adj;
    std::vector<int> cnt, in, d;
    DiffConstraints() : n(0) {}
    DiffConstraints(int n_) {
        init(n_);
    }
    void init(int n_) {
        n = n_;
        adj.resize(n);
        cnt.assign(n, 0);
        in.assign(n, 0);
        d.assign(n, 0);
    }
    void add(int a, int b, int c) {
        adj[a].push_back({b, c});
    }
    // 添加约束 x_a - x_b <= c
    void addConstraint(int a, int b, int c) {
        add(b, a, c);
    }
    bool spfa(int u, int k) {
        std::queue<int> q;
        cnt.assign(n, 0);
        in.assign(n, 0);
        q.push(u);
        in[u] = 1;
        while (!q.empty()) {
            int u = q.front();
            q.pop();
            in[u] = 0;
            for (const auto& [v, w] : adj[u]) {
                if (d[v] < d[u] + w * k) {
                    d[v] = d[u] + w * k;
                    if (!in[v]) {
                        if (++cnt[v] > n) return false;
                        in[v] = 1;
                        q.push(v);
                    }
                }
            }
        }
        return true;
    }
    //求解最小值（最长路）(即spfa边权转化为负的跑最短路)
    bool solveMin(int u = 0) {
        d.assign(n, -0x3f3f3f3f);
        d[u] = 0;
        return spfa(u, -1);
    }
    //求解最大值（最短路）
    bool solveMax(int u = 0) {
        d.assign(n, 0x3f3f3f3f);
        d[u] = 0;
        return spfa(u, 1);
    }
    int dis(int x) {
        return d[x];
    }
};