不开O2 A了，开了之后0分（WA on answer too short)，求助

#include<bits/stdc++.h>
#define int long long
using namespace std;
const int N=5e5+10;
int n,m,a[N];
struct node{
	int l,r,sum,rsum,lsum,msum;
	node* left;
	node *right;
};
void build(node* prs,int l,int r){
	prs->l=l;
	prs->r=r;
	if(l==r){
//		if(a[l]>0){
		prs->lsum=prs->msum=prs->rsum=a[l];
//		}
//		else{
//			prs->lsum=prs->msum=prs->rsum=0;
//		}
		prs->sum=a[l];
		return ;
	}
	prs->left=new node;
	prs->right=new node;
	int mid=(l+r)>>1;
	build(prs->left,l,mid);
	build(prs->right,mid+1,r);
	prs->sum=prs->left->sum+prs->right->sum;
	prs->lsum=max(prs->left->lsum,prs->left->sum+prs->right->lsum);
	prs->rsum=max(prs->right->rsum,prs->right->sum+prs->left->rsum);
	prs->msum=max(prs->left->rsum+prs->right->lsum,max(prs->left->msum,prs->right->msum)); 
}
void change(node* prs,int l,int v){
	if(prs->l==prs->r&&prs->l==l){
		prs->sum=v;
//		if(v>0){
		prs->lsum=prs->msum=prs->rsum=v;
//		}
//		else{
//			prs->lsum=prs->msum=prs->rsum=0;
//		}
		return ;
	}
	int mid=(prs->l+prs->r)>>1;
	if(l<=mid){
		change(prs->left,l,v);
	}
	if(l>mid){
		change(prs->right,l,v);
	}
	prs->sum=prs->left->sum+prs->right->sum;
	prs->lsum=max(prs->left->lsum,prs->left->sum+prs->right->lsum);
	prs->rsum=max(prs->right->rsum,prs->right->sum+prs->left->rsum);
	prs->msum=max(prs->left->rsum+prs->right->lsum,max(prs->left->msum,prs->right->msum)); 
}
node serch(node* prs,int l,int r){
	if(l<=prs->l&&r>=prs->r){
		node a;
		a.lsum=prs->lsum;a.msum=prs->msum;
		a.rsum=prs->rsum;a.sum=prs->sum;
		return a;
	}
	int mid=(prs->l+prs->r)>>1;
	bool ha=0,hb=0;
	node a,b,k;
	k.sum=0;
	a.rsum=a.lsum=a.msum=a.sum=b.rsum=b.lsum=b.msum=b.sum=0;
	if(l<=mid){
		a=serch(prs->left,l,r);
		ha=1;
	}
	if(r>mid){
		b=serch(prs->right,l,r);
		hb=1;
	}
	if(ha&&!hb){
		return a;
	}
	if(!ha&&hb){
		return b;
	}
	if(ha&&hb){
		k.msum=max(max(a.msum,b.msum),a.rsum+b.lsum);
		k.rsum=max(b.rsum,a.rsum+b.sum);
		k.lsum=max(a.lsum,a.sum+b.lsum);
		k.sum=a.sum+b.sum;
		return k;
	}
}
signed main(){
	scanf("%lld%lld",&n,&m);
	for(int i=1;i<=n;i++){
		scanf("%lld",&a[i]);
	}
	node* root=new node;
	build(root,1,n);
	int q1,q2,q3;
	for(int i=1;i<=m;i++){
		scanf("%d%lld%lld",&q1,&q2,&q3);
		if(q1==1){
			if(q2>q3){
				swap(q2,q3);
			}
			printf("%lld\n",serch(root,q2,q3).msum);
		}
		else{
			change(root,q2,q3);
		}
	}
}