题意（以 P2710 为例）
思路
使用 FHQ-Treap 进行求解，清晰明了。
- 对于 insert，先将要插入的数建成一棵树，然后将这棵树放入 FHQ-Treap 中。
- 对于 delete，将要删除的树分离出来，然后把剩下的部分合并即可，将删除的树的树根丢到废弃节点的栈中以备以后使用（节约空间，不然 MLE）。
- 对于 reverse，给一个节点打上标签并立即交换，参考文艺平衡树代码。注意，如果存在
MAKE-SAME操作的标签，那么不用反转，因为所有数字都是一样的。 - 对于 make-same，将这个节点的 reverse 的标记清空（用不到，理由如上），给这个节点打上标记并立即更新结构体中所有数字。
- 对于 get-sum，pushup 维护即可。
- 对于 get，与普通平衡树的看排名为 \(x\) 的数字是什么类似。
- 对于 max-sum，最大子段和，参考 GSS-1，注意这是平衡树，对于根节点的处理细节非常多。
代码
细节非常多，注意对废弃节点的处理。（代码以 P2710 为准）
#include <bits/stdc++.h>using namespace std;
using i64 = long long;const int N = 500010;
const i64 inf = 1e18;struct node {int l, r, size, rnd;int tag_same, tag_rev;i64 key, lsum, rsum, sum, ans;
} tr[N];int rt, cnt;
int del_ver[N], top;
int n, m;
int a[N], sz_a;int newnode(int key) {int idx;if (!top) idx = ++cnt;else {idx = del_ver[top];top--;if (tr[idx].l) del_ver[++top] = (tr[idx].l);if (tr[idx].r) del_ver[++top] = (tr[idx].r);}tr[idx].l = tr[idx].r = 0;tr[idx].rnd = rand();tr[idx].size = 1;tr[idx].tag_same = -1e9;tr[idx].tag_rev = 0;tr[idx].key = tr[idx].lsum = tr[idx].rsum = tr[idx].sum = tr[idx].ans = key;return idx;
}void addtagrev(int u) {if (!u) return;if (tr[u].tag_same != -1e9) return;tr[u].tag_rev ^= 1;swap(tr[u].l, tr[u].r);swap(tr[u].lsum, tr[u].rsum);
}void addtagsame(int u, int key) {if (!u) return;if (tr[u].tag_rev) tr[u].tag_rev = 0;tr[u].tag_same = tr[u].key = key;tr[u].sum = key * tr[u].size;tr[u].lsum = tr[u].rsum = tr[u].ans = max(tr[u].key, tr[u].sum);
}void pushdown(int u) {if (tr[u].tag_same != -1e9) {tr[u].tag_rev = 0;addtagsame(tr[u].l, tr[u].tag_same);addtagsame(tr[u].r, tr[u].tag_same);tr[u].tag_same = -1e9;}if (tr[u].tag_rev) {addtagrev(tr[u].l);addtagrev(tr[u].r);tr[u].tag_rev = 0;}
}void pushup(int u) {tr[u].size = tr[tr[u].l].size + tr[tr[u].r].size + 1;tr[u].lsum = max({tr[tr[u].l].lsum, tr[tr[u].l].sum + tr[u].key, tr[tr[u].l].sum + tr[tr[u].r].lsum + tr[u].key});tr[u].rsum = max({tr[tr[u].r].rsum, tr[tr[u].r].sum + tr[u].key, tr[tr[u].r].sum + tr[tr[u].l].rsum + tr[u].key});tr[u].sum = tr[tr[u].l].sum + tr[tr[u].r].sum + tr[u].key;tr[u].ans = max({tr[tr[u].l].ans, tr[tr[u].r].ans, tr[u].key, tr[tr[u].l].rsum + tr[u].key, tr[tr[u].r].lsum + tr[u].key, tr[tr[u].l].rsum + tr[u].key + tr[tr[u].r].lsum});
}void split(int u, int sz, int &x, int &y) {if (!u) {x = y = 0;return;}pushdown(u);if (tr[tr[u].l].size + 1 <= sz) {x = u;split(tr[u].r, sz - tr[tr[u].l].size - 1, tr[u].r, y);}else {y = u;split(tr[u].l, sz, x, tr[u].l);}pushup(u);
}int merge(int x, int y) {if ((!x) || (!y)) return x | y;if (tr[x].rnd < tr[y].rnd) {pushdown(x);tr[x].r = merge(tr[x].r, y);pushup(x);return x;}else {pushdown(y);tr[y].l = merge(x, tr[y].l);pushup(y);return y;}
}void del(int l, int r) {int x, y, z;split(rt, r, x, z);split(x, l - 1, x, y);del_ver[++top] = (y);rt = merge(x, z);
}int build(int l, int r) {if (l == r) return newnode(a[l]);int mid = (l + r) >> 1;int x = build(l, mid);int y = build(mid + 1, r);return merge(x, y);
}void insert(int p) {int x, y;int rt2 = build(1, sz_a);split(rt, p, x, y);rt = merge(merge(x, rt2), y);
}void make_same(int l, int r, int c) {int x, y, z;split(rt, r, x, z);split(x, l - 1, x, y);addtagsame(y, c);rt = merge(merge(x, y), z);
}void reverse_arr(int l, int r) {int x, y, z;split(rt, r, x, z);split(x, l - 1, x, y);addtagrev(y);rt = merge(merge(x, y), z);
}i64 get_sum(int l, int r) {int x, y, z;split(rt, r, x, z);split(x, l - 1, x, y);i64 ans = tr[y].sum;rt = merge(merge(x, y), z);return ans;
}i64 get_max(int l, int r) {int x, y, z;split(rt, r, x, z);split(x, l - 1, x, y);i64 ans = tr[y].ans;rt = merge(merge(x, y), z);return ans;
}int get_num(int u, int rk) {pushdown(u);if (tr[tr[u].l].size + 1 == rk) return tr[u].key;else if (tr[tr[u].l].size >= rk) return get_num(tr[u].l, rk);else return get_num(tr[u].r, rk - tr[tr[u].l].size - 1);
}int main() {ios::sync_with_stdio(false);cin.tie(nullptr);cin >> n >> m;tr[0].lsum = tr[0].rsum = tr[0].ans = -inf;for (int i = 1; i <= n; i++) cin >> a[i];sz_a = n;insert(0);string opt;int x, y, z;for (int T = 1; T <= m; T++) {cin >> opt;if (opt == "INSERT") {cin >> x >> sz_a;for (int i = 1; i <= sz_a; i++) cin >> a[i];insert(x);}else if (opt == "DELETE") {cin >> x >> y;del(x, x + y - 1);}else if (opt == "MAKE-SAME") {cin >> x >> y >> z;make_same(x, x + y - 1, z);}else if (opt == "REVERSE") {cin >> x >> y;reverse_arr(x, x + y - 1);}else if (opt == "GET-SUM") {cin >> x >> y;cout << get_sum(x, x + y - 1) << '\n';}else if (opt == "GET") {cin >> x;cout << get_num(rt, x) << '\n';}else {cin >> x >> y;cout << get_max(x, x + y - 1) << '\n';}}return 0;
}
