python/TangDou/AcWing/SegmentTree/SPOJ_GSS5.cpp

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <iostream>

using namespace std;
const int N = 10010;

int a[N];
struct Node {
    int l, r;
    int sum, tmax, lmax, rmax;
} tr[N << 2];

void calc(Node &u, Node &l, Node &r) {
    u.sum = l.sum + r.sum;                           // 区间和
    u.tmax = max({l.tmax, r.tmax, l.rmax + r.lmax}); // 子区间最大值
    u.lmax = max(l.lmax, l.sum + r.lmax);            // 左前缀最大值
    u.rmax = max(r.rmax, r.sum + l.rmax);            // 右后缀最大值
}
void pushup(int u) {
    calc(tr[u], tr[u << 1], tr[u << 1 | 1]);
}

void build(int u, int l, int r) {
    tr[u] = {l, r, 0, 0, 0, 0};

    if (l == r) {
        tr[u].sum = tr[u].tmax = tr[u].lmax = tr[u].rmax = a[l];
        return;
    }

    int mid = (tr[u].l + tr[u].r) >> 1;
    build(u << 1, l, mid), build(u << 1 | 1, mid + 1, r);
    pushup(u);
}

Node query(int u, int l, int r) {
    if (l > tr[u].r || r < tr[u].l) return {}; // 递归出口，不在我管辖范围内的情况，返回0
    if (l <= tr[u].l && tr[u].r <= r) return tr[u];

    int mid = (tr[u].l + tr[u].r) >> 1;
    if (r <= mid) return query(u << 1, l, r);
    if (l > mid) return query(u << 1 | 1, l, r);

    Node a = query(u << 1, l, r), b = query(u << 1 | 1, l, r), c;
    calc(c, a, b);
    return c;
}
int main() {
    // 加快读入
    ios::sync_with_stdio(false), cin.tie(0);

    int T, n, m;
    cin >> T;
    while (T--) {
        cin >> n;
        for (int i = 1; i <= n; i++) cin >> a[i];
        build(1, 1, n);

        cin >> m;
        while (m--) {
            int x1, y1, x2, y2, res;
            Node a, b, c;
            cin >> x1 >> y1 >> x2 >> y2;
            if (y1 < x2) { // 这里不能取等 不然边界会被算2次
                a = query(1, x1, y1);
                b = query(1, x2, y2);
                c = query(1, y1 + 1, x2 - 1);
                res = a.rmax + c.sum + b.lmax;
            } else {
                res = query(1, x2, y1).tmax; // 最大子序列和出现在交集中

                a = query(1, x1, x2 - 1);
                b = query(1, x2, y2);
                res = max(res, a.rmax + b.lmax);

                a = query(1, x1, y1);
                b = query(1, y1 + 1, y2);
                res = max(res, a.rmax + b.lmax);
            }
            printf("%d\n", res);
        }
    }
    return 0;
}