题解

题面大意：

使用平衡树维护一个数列，支持插入，修改，删除，翻转，求和，求最大和这 (6) 个操作.

题意分析：

Splay 裸题，几乎各种操作都有了，这个代码就发给大家当个模板吧.

最后求最大和的时候可以事先维护好最大和，然后输出即可。

代码：

#include <cstdio>
#include <climits>
#include <algorithm>
#include <iostream>
#define maxn 1000001
using namespace std;

inline int read() {
    int x = 0;
    bool f = 0; char c = getchar();
    while (c < '0' || c > '9') {if (c == '-') f = 1; c = getchar();}
    while ('0' <= c && c <= '9') {x = (x << 3) + (x << 1) + (c ^ 48); c = getchar();}
    if (f) {
        x = -x;
    }
    return x;
}

int stack[maxn], top, v[maxn];
struct Splay {
#define T(x) (tree[f[x]][1]==x)
#define ls(x) tree[x][0]
#define rs(x) tree[x][1]
	int tree[maxn][2], f[maxn], size[maxn], val[maxn];
	int sum[maxn], L[maxn], R[maxn], Max[maxn];
	bool rev[maxn], mark[maxn];
	int root, len;
    
	void cov_tag(int x, int v) {
		if (!x)	return;
		sum[x] = size[x] * v;
		val[x] = v;
		L[x] = R[x] = Max[x] = max(v, sum[x]);
		mark[x] = 1, rev[x] = 0;
	}
    
	void rev_tag(int x) {
		if (!x)	return;
		swap(L[x], R[x]);
		swap(ls(x), rs(x));
		rev[x] ^= 1;
	}
    
	void pushdown(int x) {
		if (rev[x]) {
			rev_tag(ls(x));
			rev_tag(rs(x));
			rev[x] = 0;
		}
		if (mark[x]) {
			cov_tag(ls(x), val[x]),
				cov_tag(rs(x), val[x]);
			mark[x] = 0;
		}
	}
    
	void updata(int x) {
		size[x] = size[ls(x)] + size[rs(x)] + 1;
		Max[x] = max(max(Max[ls(x)], Max[rs(x)]), max(0, R[ls(x)]) + val[x] + max(0, L[rs(x)]));
		L[x] = max(L[ls(x)], sum[ls(x)] + val[x] + max(0, L[rs(x)]));
		R[x] = max(R[rs(x)], sum[rs(x)] + val[x] + max(0, R[ls(x)]));
		sum[x] = sum[ls(x)] + sum[rs(x)] + val[x];
	}
    
	int get() {
		int x;
		x = top ? stack[top--] : ++len;
		ls(x) = rs(x) = f[x] = 0;
		rev[x] = mark[x] = 0;
		size[x] = 1;
		sum[x] = L[x] = R[x] = val[x] = -1e9;
		return x;
	}
    
	void build(int fa, int l, int r, int& x) {
		if (l > r)	return;
		int mid = (l + r) >> 1;
		x = get(), f[x] = fa, val[x] = v[mid];
		if (l == r) {
			size[x] = 1;
			Max[x] = L[x] = R[x] = sum[x] = val[x];
			return;
		}
		build(x, l, mid - 1, ls(x));
		build(x, mid + 1, r, rs(x));
		updata(x);
	}
    
	void init(int n) {
		L[0] = R[0] = Max[0] = -1e9;
		len = 2, root = 1;
		rs(1) = size[1] = 2, L[1] = R[1] = val[1] = sum[1] = -1e9;
		f[2] = size[2] = 1, L[2] = R[2] = val[2] = sum[2] = -1e9;
		for (int i = 1; i <= n; i++)	v[i] = read();
		build(2, 1, n, ls(2));
		updata(2), updata(1);
	}
    
	void move(int x) {
		int fa = f[x], son = tree[x][T(x) ^ 1];
		tree[x][T(x) ^ 1] = fa;
		tree[fa][T(x)] = son;
		if (son)	f[son] = fa;
		f[x] = f[fa];
		if (f[x])	tree[f[x]][T(fa)] = x;
		f[fa] = x;
		updata(fa);
        updata(x);
	}
    
	void splay(int x) {
		while (f[x]) {
			if (f[f[x]])	T(x) == T(f[x]) ? move(f[x]) : move(x);
			move(x);
		}
		root = x;
	}
    
	int find(int x, int i) {
		pushdown(i);
		if (size[ls(i)] + 1 == x)	return i;
		if (x <= size[ls(i)])	return find(x, ls(i));
		return find(x - size[ls(i)] - 1, rs(i));
	}
    
	void insert() {
		int x = read() + 1, y = x + 1, tot = read();
		x = find(x, root), splay(x);
		y = find(y, root), splay(y);
		if (f[x] != root)	move(x);
		for (int i = 1; i <= tot; i++)	v[i] = read();
		build(x, 1, tot, rs(x));
		updata(x);
        updata(y);
	}
    
	void reuse(int x) {
		if (!x)	return;
		stack[++top] = x;
		reuse(ls(x));
        reuse(rs(x));
	}
    
	void Del() {
		int x = read(), y = read() + x - 1;
		x = find(x, root), splay(x);
		y = find(y + 2, root), splay(y);
		if (f[x] != root)	move(x);
		reuse(rs(x));
		f[rs(x)] = 0, rs(x) = 0;
		updata(x);
        updata(y);
	}
    
	void cover() {
		int x = read(), y = read() + x - 1, v = read();
		x = find(x, root), splay(x);
		y = find(y + 2, root), splay(y);
		if (f[x] != root)	move(x);
		cov_tag(rs(x), v);
		updata(x);
        updata(y);
	}
    
	void reverse() {
		int x = read(), y = read() + x - 1;
		x = find(x, root), splay(x);
		y = find(y + 2, root), splay(y);
		if (f[x] != root)	move(x);
		rev_tag(rs(x));
		updata(x);
        updata(y);
	}
    
	void query_sum() {
		int x = read(), y = read() + x - 1;
		x = find(x, root), splay(x);
		y = find(y + 2, root), splay(y);
		if (f[x] != root)	move(x);
		printf("%d
", sum[rs(x)]);
	}
    
	void query_max() { 
        printf("%d
", Max[root]); 
    }
} splay;

int main()
{
    freopen("sequence.in", "r", stdin);
    freopen("sequence.out", "w", stdout);
	int n, m;
	scanf("%d %d", &n, &m);
	splay.init(n); // 先插入 n 个数并建立平衡树
	while (m--)
	{
		string ss;
		cin >> ss;

		if (ss[0] == 'I') { // 插入操作
			splay.insert();
		}
		if (ss[0] == 'D') { // 删除操作
			splay.Del();
		}
		if (ss[0] == 'M' && ss[2] == 'K') { // 修改操作
			splay.cover();
		}
		if (ss[0] == 'R') { // 旋转操作
			splay.reverse();
		}
		if (ss[0] == 'G') { // 求和操作
			splay.query_sum();
		}
		if (ss[0] == 'M' && ss[2] == 'X') { // 修改操作
			splay.query_max();
		}
	}
	return 0;
}