维护数列 https://www.acwing.com/problem/content/957/
线段树能写的splay都能写，不过splay常数较大。时间复杂度大概是线段树的三倍

#include<bits/stdc++.h>
using namespace std;
const int N = 500010,INF = 1e9;
int n,m;
struct Node
{int s[2],p,v;int rev,same;int size,sum,ms,ls,rs;void init(int _v,int _p)//初始化点{s[0] = s[1] = 0,p = _p,v = _v;rev = same = 0;size = 1,sum = ms = v;ls = rs = max(v,0);}
}tr[N];int root,nodes[N],tt;
int w[N];void pushup(int x)
{auto &u = tr[x], &l = tr[u.s[0]], &r = tr[u.s[1]];u.size = l.size + r.size + 1;u.sum = l.sum + r.sum + u.v;u.ls = max(l.ls, l.sum + u.v + r.ls);u.rs = max(r.rs, r.sum + u.v + l.rs);u.ms = max(max(l.ms, r.ms), l.rs + u.v + r.ls);
}void pushdown(int x)
{auto &u = tr[x], &l = tr[u.s[0]], &r = tr[u.s[1]];if (u.same){u.same = u.rev = 0;if (u.s[0]) l.same = 1, l.v = u.v, l.sum = l.v * l.size;if (u.s[1]) r.same = 1, r.v = u.v, r.sum = r.v * r.size;if (u.v > 0){if (u.s[0]) l.ms = l.ls = l.rs = l.sum;if (u.s[1]) r.ms = r.ls = r.rs = r.sum;}else{if (u.s[0]) l.ms = l.v, l.ls = l.rs = 0;if (u.s[1]) r.ms = r.v, r.ls = r.rs = 0;}}else if (u.rev){u.rev = 0, l.rev ^= 1, r.rev ^= 1;swap(l.ls, l.rs), swap(r.ls, r.rs);swap(l.s[0], l.s[1]), swap(r.s[0], r.s[1]);}
}
void rotate(int x)
{int y = tr[x].p,z = tr[y].p;int k = tr[y].s[1] == x;//看是y的哪个儿子tr[z].s[tr[z].s[1]==y] = x,tr[x].p = z;tr[y].s[k] = tr[x].s[k^1],tr[tr[x].s[k^1]].p = y;tr[x].s[k^1] = y,tr[y].p = x;pushup(y);pushup(x);
}
void splay(int x,int k)//转到k的下面
{while (tr[x].p!=k){int y = tr[x].p,z = tr[y].p;if (z!=k) if ((tr[y].s[1]==x)^(tr[z].s[1]==y)) rotate(x);//如果不是直线型，那么就转两次xelse rotate(y);rotate(x);}if (!k) root = x;//如果转到顶了
}
int get_k(int k)//第k大个数的坐标
{int u = root;while (u){pushdown(u);if (tr[tr[u].s[0]].size>=k) u = tr[u].s[0];else if (tr[tr[u].s[0]].size+1==k) return u;else k-=tr[tr[u].s[0]].size+1,u = tr[u].s[1];}
}
int build(int l,int r,int p)//模仿线段树建树
{int mid = l+r>>1;int u = nodes[tt--];tr[u].init(w[mid],p);if (l<mid) tr[u].s[0] = build(l,mid-1,u);if (r>mid) tr[u].s[1] = build(mid+1,r,u);pushup(u);return u;
}
void dfs(int u)
{if (tr[u].s[0]) dfs(tr[u].s[0]);if (tr[u].s[1]) dfs(tr[u].s[1]);nodes[ ++ tt ] = u;//删除回收机制
}
int main()
{for (int i = 1;i<N;i++) nodes[++tt] = i;scanf("%d%d",&n,&m);tr[0].ms = w[0] = w[n+1] = -INF;//哨兵for (int i = 1;i<=n;i++) scanf("%d",&w[i]);root = build(0,n+1,0);char op[20];while (m--){scanf("%s",op);if (!strcmp(op,"INSERT")){int posi,tot;scanf("%d%d",&posi,&tot);for (int i = 0;i<tot;i++) scanf("%d",&w[i]);int l = get_k(posi+1),r = get_k(posi+2);splay(l,0);splay(r,l);int u = build(0,tot-1,r);tr[r].s[0] = u;pushup(r);pushup(l);}else if (!strcmp(op,"DELETE")){int posi,tot;scanf("%d%d",&posi,&tot);int l = get_k(posi),r = get_k(posi+tot+1);splay(l,0),splay(r,l);dfs(tr[r].s[0]);tr[r].s[0] = 0;pushup(r);pushup(l);}else if (!strcmp(op,"MAKE-SAME")){int posi,tot,c;scanf("%d%d%d",&posi,&tot,&c);int l = get_k(posi),r = get_k(posi+tot+1);splay(l,0);splay(r,l);auto &son = tr[tr[r].s[0]];son.same = 1,son.v = c,son.sum = c * son.size;if (c>0) son.ms = son.ls = son.rs = son.sum;else son.ms = c,son.ls = son.rs = 0;pushup(r);pushup(l);}else if (!strcmp(op, "REVERSE")){int posi,tot;scanf("%d%d",&posi,&tot);int l = get_k(posi),r = get_k(posi+tot+1);splay(l,0);splay(r,l);auto &son = tr[tr[r].s[0]];son.rev^=1;swap(son.ls,son.rs);swap(son.s[0],son.s[1]);pushup(r);pushup(l);}else if (!strcmp(op, "GET-SUM")){int posi,tot;scanf("%d%d",&posi,&tot);int l = get_k(posi), r = get_k(posi + tot + 1);splay(l, 0), splay(r, l);printf("%d\n", tr[tr[r].s[0]].sum);}else printf("%d\n",tr[root].ms);}
}**