题目：http://www.lydsy.com:808/JudgeOnline/problem.php?id=1251

代码（用splay树维护区间，注意每次不是直接splay(l-1,roof),splay(r+1,R[roof])而是splay(select(l-1,roof),roof),splay(select(r+1,R[roof]),R[roof])）:

#include <cstdio>
#include <algorithm>
#include <cstring>
#include <cstdlib>
using namespace std;
#define MAXN 50010
#define L(t) T[t].left
#define R(t) T[t].right
#define M(t) T[t].Max
#define D(t) T[t].delta
#define F(t) T[t].flag
#define S(t) T[t].size
#define K(t) T[t].key
#define C(r,t) (S(L(t))>r)
#define inf 0x7fffffff
struct node {
        int left,right,Max,delta,size,key;
        bool flag;
        node(){left=right=delta=flag=size=Max=key=0;}
} T[MAXN];
int roof=0,v=0,n,m;
void Insert(int &t) {
        if (!t){S(t=++v)=1;return ;}
        S(t)++; Insert(R(t));
}
void pushdown(int t) {
        if (t){
               if (F(t))
                  {swap(L(t),R(t));F(L(t))^=true,F(R(t))^=true;F(t)^=true;}
               if (D(t))
                  {M(t)+=D(t),K(t)+=D(t);D(L(t))+=D(t),D(R(t))+=D(t);D(t)=0;}
        }
}
void update(int t) 
{pushdown(L(t)),pushdown(R(t));S(t)=S(L(t))+S(R(t))+1;M(t)=max(max(M(L(t)),M(R(t))),K(t));}
void zag(int &t) {
        int k;pushdown(t);pushdown(k=R(t));
        R(t)=L(k);update(t);L(k)=t;update(k);
        t=k;
}
void zig(int &t) {
        int k;pushdown(t);pushdown(k=L(t));
        L(t)=R(k);update(t);R(k)=t;update(k);
        t=k;
}
bool splay(int r,int &t,bool flag) {
        pushdown(t);
        if (S(L(t))==r) return false;
        bool w=splay(C(r,t)?r:r-S(L(t))-1,C(r,t)?L(t):R(t),true);
        if (!w){if (!flag){if (C(r,t)) zig(t); else zag(t);}
        } else {
               if (C(r,t)) 
                   {pushdown(L(t));if (C(r,L(t))) zig(t) ; else zag(L(t));zig(t);} else
            {pushdown(R(t));if (!C(r-S(L(t))-1,R(t))) zag(t) ; else zig(R(t));zag(t);}
        }
        return w^true;
}
int main() {
        M(0)=-inf;
        scanf("%d%d",&n,&m);
        for (int i=0;i<=n+1;i++) Insert(roof),splay(i,roof,false);
        while (m--) {
               int x,l,r;
               scanf("%d%d%d",&x,&l,&r);
               splay(l-1,roof,false);splay(r-S(L(roof)),R(roof),false);
               pushdown(roof);pushdown(R(roof));pushdown(L(R(roof)));
               if (x==1) {scanf("%d",&x);D(L(R(roof)))+=x;} else 
               {
                       if (x==2) {F(L(R(roof)))^=true;} else printf("%d\n",M(L(R(roof))));
               }
        }
        return 0;
}