lc2382 - segtree

namespace atcoder
{

template <class S, S (*op)(S, S), S (*e)()> struct segtree {
    int ceil_pow2(int n)
    {
        int x = 0;
        while ((1U << x) < (unsigned int) (n))
            x++;
        return x;
    }

  public:
    segtree() : segtree(0) {}
    explicit segtree(int n) : segtree(std::vector<S>(n, e())) {}
    explicit segtree(const std::vector<S> &v) : _n(int(v.size()))
    {
        log = ceil_pow2(_n);
        size = 1 << log;
        d = std::vector<S>(2 * size, e());
        for (int i = 0; i < _n; i++)
            d[size + i] = v[i];
        for (int i = size - 1; i >= 1; i--) {
            update(i);
        }
    }

    void set(int p, S x)
    {
        assert(0 <= p && p < _n);
        p += size;
        d[p] = x;
        for (int i = 1; i <= log; i++)
            update(p >> i);
    }

    S get(int p) const
    {
        assert(0 <= p && p < _n);
        return d[p + size];
    }

    S prod(int l, int r) const
    {
        assert(0 <= l && l <= r && r <= _n);
        S sml = e(), smr = e();
        l += size;
        r += size;

        while (l < r) {
            if (l & 1)
                sml = op(sml, d[l++]);
            if (r & 1)
                smr = op(d[--r], smr);
            l >>= 1;
            r >>= 1;
        }
        return op(sml, smr);
    }

    S all_prod() const { return d[1]; }

    template <bool (*f)(S)> int max_right(int l) const
    {
        return max_right(l, [](S x) { return f(x); });
    }
    template <class F> int max_right(int l, F f) const
    {
        assert(0 <= l && l <= _n);
        assert(f(e()));
        if (l == _n)
            return _n;
        l += size;
        S sm = e();
        do {
            while (l % 2 == 0)
                l >>= 1;
            if (!f(op(sm, d[l]))) {
                while (l < size) {
                    l = (2 * l);
                    if (f(op(sm, d[l]))) {
                        sm = op(sm, d[l]);
                        l++;
                    }
                }
                return l - size;
            }
            sm = op(sm, d[l]);
            l++;
        } while ((l & -l) != l);
        return _n;
    }

    template <bool (*f)(S)> int min_left(int r) const
    {
        return min_left(r, [](S x) { return f(x); });
    }
    template <class F> int min_left(int r, F f) const
    {
        assert(0 <= r && r <= _n);
        assert(f(e()));
        if (r == 0)
            return 0;
        r += size;
        S sm = e();
        do {
            r--;
            while (r > 1 && (r % 2))
                r >>= 1;
            if (!f(op(d[r], sm))) {
                while (r < size) {
                    r = (2 * r + 1);
                    if (f(op(d[r], sm))) {
                        sm = op(d[r], sm);
                        r--;
                    }
                }
                return r + 1 - size;
            }
            sm = op(d[r], sm);
        } while ((r & -r) != r);
        return 0;
    }

  private:
    int _n, size, log;
    std::vector<S> d;

    void update(int k) { d[k] = op(d[2 * k], d[2 * k + 1]); }
};

} // namespace atcoder
using atcoder::segtree;
using ll = long long;
struct S {
    ll max_val;
    ll lmargin, rmargin;
    ll nz;
};
S op(S a, S b)
{
    S ret{max(a.max_val, b.max_val), a.lmargin, b.rmargin, a.nz && b.nz};
    if (a.nz) {
        ret.lmargin = a.lmargin + b.lmargin;
    }
    if (b.nz) {
        ret.rmargin = a.rmargin + b.rmargin;
    }
    ret.max_val = max(ret.max_val, max(ret.lmargin, ret.rmargin));
    ret.max_val = max(ret.max_val, a.rmargin + b.lmargin);
    return ret;
}
S e() { return S{0, 0, 0, 0}; }
class Solution
{
  public:
    vector<long long> maximumSegmentSum(vector<int> &ns, vector<int> &rq)
    {
        int n = ns.size();
        vector<ll> ret(rq.size());
        segtree<S, op, e> seg(n);
        for (int i = rq.size() - 1; i >= 0; --i) {
            ret[i] = seg.all_prod().max_val;
            ll val = ns[rq[i]];
            seg.set(rq[i], S{val, val, val, 1});
        }
        return ret;
    }
};