subsegment with max sum

struct node {
    int sum_max, suff, pref, sum;
};

node combine(node tl, node tr) {
    node res;
    res.sum = tl.sum + tr.sum;
    res.pref = max(tl.pref, tl.sum + tr.pref);
    res.suff = max(tr.suff, tr.sum + tl.suff);
    res.sum_max = max({
        tl.sum_max,
        tr.sum_max,
        tl.suff + tr.pref;
    });
    return res;
}