小白逛公园求助9pts

#include<iostream>
#include<cstdio>
using namespace std;
inline int read(){
    register int x=0,v=1,ch=getchar();
    while(!isdigit(ch)){if(ch=='-')v=-1;ch=getchar();}
    while(isdigit(ch)){x=(x<<3)+(x<<1)+(ch^'0');ch=getchar();}
    return x*v;
}
const int MAX=500005;
struct Node{
    int ml,mr,v;
    int mx;
}tree[MAX<<2]; 
int a[MAX];
inline int Max(int a,int b){return a>b?a:b;}
inline void pushup(int x){
    tree[x].v=tree[x<<1].v+tree[x<<1|1].v;
    tree[x].ml=Max(tree[x<<1].ml,tree[x<<1].v+tree[x<<1|1].ml);
    tree[x].mr=Max(tree[x<<1|1].mr,tree[x<<1|1].v+tree[x<<1].mr);
    tree[x].mx=Max(tree[x<<1].mx,Max(tree[x<<1|1].mx,tree[x<<1].mr+tree[x<<1|1].ml));
}
void build(int x,int l,int r){
    if(l==r){
        tree[x]=(Node){a[l],a[l],a[l],a[l]}; 
        return ;
    }
    register int mid=l+r>>1;
    build(x<<1,l,mid);build(x<<1|1,mid+1,r);
    pushup(x);
}
void modify(int x,int l,int r,int s,int v){
    if(l==r){
        tree[x]=(Node){v,v,v,v}; 
        return ;
    }
    register int mid=l+r>>1;
    if(s<=mid)modify(x<<1,l,mid,s,v);
    if(mid<s) modify(x<<1|1,mid+1,r,s,v);
    pushup(x); 
}
Node query(int x,int l,int r,int s,int t){
    if(s<=l&&r<=t)return tree[x];
    register int res,mid=l+r>>1;
    if(s<=mid)return query(x<<1,l,mid,s,t);
    else if(mid<t)return query(x<<1|1,mid+1,r,s,t);
    else {
        Node p=query(x<<1,l,mid,s,t),q=query(x<<1|1,mid+1,r,s,t),k;
        k.v=p.v+q.v;
        k.ml=Max(p.v+q.ml,p.ml);
        k.mr=Max(q.v+p.mr,q.mr);
        k.mx=Max(p.mr+q.ml,Max(q.mx,p.mx));
        return k;
    }
}
int m,n,op,l,r; 
signed main(){
    n=read();m=read();
    for(register int i=1;i<=n;++i){
        a[i]=read();
    }
    build(1,1,n);
    while(m--){
        op=read();
        l=read(),r=read();
        if(op==1){
            if(l>r)swap(l,r);
            Node tmp=query(1,1,n,l,r);
            printf("%d\n",tmp.mx);
        }else{
            modify(1,1,n,l,r);
        }
    }
    return 0;
}