求助

#include<bits/stdc++.h>
using namespace std;
const int N = 5e5 + 10;
int n,m;
int a[N];
struct node{
    int l,r;
    int sum;
    int maxx,qmaxx,hmaxx;
}tr[4 * N];
void push_up(int u){
   tr[u].sum = tr[u << 1].sum + tr[u << 1 | 1].sum;
   tr[u].maxx = max(max(tr[u << 1].maxx,tr[u << 1 | 1].maxx),tr[u << 1].hmaxx + tr[u << 1 | 1].qmaxx);
   tr[u].qmaxx = max(tr[u << 1].qmaxx,tr[u << 1].sum + tr[u << 1 | 1].qmaxx);
   tr[u].hmaxx = max(tr[u << 1 | 1].hmaxx,tr[u << 1].hmaxx + tr[u << 1 | 1].sum);
}
void pushup(node &u,node &l,node &r){
    u.sum = l.sum + r.sum;
    u.qmaxx = max(l.qmaxx,l.sum + r.qmaxx);
    u.hmaxx = max(r.hmaxx,r.sum + l.hmaxx);
    u.maxx = max(max(l.maxx,r.maxx),l.hmaxx + r.qmaxx);
}
void build(int u,int l,int r){
    tr[u].l = l,tr[u].r = r;
    if(l == r){
        tr[u].sum = tr[u].qmaxx = tr[u].hmaxx = tr[u].maxx = a[l];
        return;
    }
    int mid = l + r >> 1;
    build(u << 1,l,mid);
    build(u << 1 | 1,mid + 1,r);
    push_up(u); 
}
void modify(int u,int a,int b){
    if(tr[u].l == a && tr[u].r == a){
        tr[u].sum = tr[u].maxx = tr[u].qmaxx = tr[u].hmaxx = b;
        return;
    }
    int mid = tr[u].l + tr[u].r >> 1;
    if(a <= mid) modify(u << 1,a,b);
    else modify(u << 1 | 1,a,b);
    push_up(u);
}
node query(int u,int l,int r){
    cout << 1 << " ";
    if(tr[u].l >= l && r >= tr[u].r){
        return tr[u];
    }
    int mid = tr[u].l + tr[u].r >> 1;
     if(l > mid) return query(u << 1,l,r);
     else if(r <= mid)  return query(u << 1 | 1,l,r);
     else {
        node left = query(u << 1,l,r);
        node right = query(u << 1 | 1,l,r);
        node ans;
        pushup(ans,left,right);
        return ans;
     }
}
int main(){
    cin >> n >> m;
    for(int i = 1; i <= n ; i++) cin >> a[i];
    build(1,1,n);
    while(m--){
        int k,a,b;
        cin >> k >> a >> b;
         if(k == 1){
          if(a > b) swap(a,b);
          cout << query(1,a,b).maxx << endl;
        }
        else{
            modify(1,a,b);
        }
    }
    return 0;
}