我感觉伸展树越来越模版了，没想到这么轻易的就过了。。。
把光标位置标记为pos
MOVE：pos++或者pos--
INSERT：把光标旋转至根部，然后把光标后一个字母旋转至根的右子树，然后把insert的内容插入到root的右子树的左子树
ROTATE：把光标旋转至根部，然后把光标后一个字母旋转至根的右子树，然后把rev[root10]取反
GET：得到光标位置的后继，可以GET_KTH后然后GET_NEXT，也可以直接旋转，或者旋转后GET_MIN
PREV,NEXT：都只需要改变光标位置变量
#include<stdio.h>
#include<string.h>
#include<algorithm>
#include<iostream>
#include<vector>
using namespace std;
#define maxn 5500000
#define mem(a,b) memset(a,b,sizeof(a))
#define root10 ch[ch[root][1]][0]
#define root1 ch[root][1]
int pre[maxn],ch[maxn][2],root,tot;
int size[maxn];
int rev[maxn];
int key[maxn];
int n;
int pos;
void Treaval(int x) {if(x) {Treaval(ch[x][0]);printf("结点%2d:左儿子 %2d 右儿子 %2d 父结点 %2d size = %2d ,key = %2d \n",x,ch[x][0],ch[x][1],pre[x],size[x],key[x]);Treaval(ch[x][1]);}
}
void debug() {printf("%d\n",root);Treaval(root);}
//以上Debug
void init()
{root=tot=0;mem(pre,0);mem(ch,0);mem(size,0);mem(rev,0);mem(key,0);
}
void newnode(int &x,char k,int father)
{x=++tot;pre[x]=father;size[x]=1;ch[x][0]=ch[x][1]=0;rev[x]=0;key[x]=k;
}
void push_down(int x)
{if(rev[x]){rev[x]=0;rev[ch[x][0]]^=1;rev[ch[x][1]]^=1;swap(ch[x][0],ch[x][1]);}
}
void push_up(int x)
{size[x]=size[ch[x][0]]+size[ch[x][1]]+1;
}
void rot(int x,int kind)
{int y=pre[x];push_down(y);push_down(x);ch[y][!kind]=ch[x][kind];pre[ch[x][kind]]=y;if(pre[y])ch[pre[y]][ch[pre[y]][1]==y]=x;pre[x]=pre[y];ch[x][kind]=y;pre[y]=x;push_up(y);push_up(x);
}
void splay(int x,int goal)
{push_down(x);while(pre[x]!=goal){if(pre[pre[x]]==goal){push_down(pre[x]);push_down(x);rot(x,ch[pre[x]][0]==x);}else{int y=pre[x];push_down(pre[y]);push_down(y);push_down(x);int kind=ch[pre[y]][0]==y;if(ch[y][kind]==x){rot(x,!kind);rot(x,kind);}else{rot(y,kind);rot(x,kind);}}}push_up(x);if(goal==0)root=x;
}
void buildtree(int &x,int l,int r,int father,char str[])
{if(l>r)return ;int mid=(l+r)/2;newnode(x,str[mid],father);buildtree(ch[x][0],l,mid-1,x,str);buildtree(ch[x][1],mid+1,r,x,str);push_up(x);
}
int get_kth(int x,int k)
{push_down(x);int p=size[ch[x][0]];if(p+1==k)return x;else if(k<=p)return get_kth(ch[x][0],k);else get_kth(ch[x][1],k-p-1);
}
int get_min(int r){push_down(r);while(ch[r][0]){r=ch[r][0];push_down(r);}return r;
}
int get_max(int r){push_down(r);while(ch[r][1]){r=ch[r][1];push_down(r);}return r;
}
void insert(char str[])
{int len=strlen(str);int x=get_kth(root,pos);//debug();// cout<<x<<" "<<root<<endl;splay(x,0);//cout<<"_-"<<endl;int m=get_min(root1);splay(m,root);buildtree(root10,0,len-1,root1,str);
}
void del(int k)
{int x=get_kth(root,pos);splay(x,0);int y=get_kth(root,pos+k+1);splay(y,root);pre[root10]=0;root10=0;push_up(root1);push_up(root);
}
void revs(int k){int x=get_kth(root,pos);splay(x,0);int y=get_kth(root,pos+k+1);splay(y,root);rev[root10]^=1;
}
int get_ans(){int x=get_kth(root,pos);splay(x,0);int y=get_min(root1);return key[y];
}
char str[maxn];
int main()
{scanf("%d",&n);init();newnode(root,' ',0);newnode(root1,' ',root);pos=1;int k;while(n--){scanf("%s",str);if(str[0]=='I'){scanf("%d",&k);getchar();gets(str);insert(str);}else if(str[0]=='M'){scanf("%d",&k);pos=k+1;}else if(str[0]=='D'){scanf("%d",&k);del(k);}else if(str[0]=='R'){scanf("%d",&k);revs(k);}else if(str[0]=='G')printf("%c\n",get_ans());else if(str[0]=='P')pos--;elsepos++;}return 0;
}