我解决了代码中显示的给定问题，但我得到了错误的答案。我使用了分段树方法。节点包含 max1（给定范围内的最大数量）和 sum（给定范围内两个数量的最大总和）。请帮忙。
#include<iostream>
#include<cstdio>
#include<math.h>
using namespace std;
struct node
{
long long int max1;
long long int sum;
};
node constructstutil(int a[],node tree[],int st,int end,int index)
{
if(st==end)
{
tree[index].max1=a[st];
tree[index].sum=a[st];
return tree[index];
}
int mid=(st+end)/2;
node i=constructstutil(a,tree,st,mid,2*index+1);
node j=constructstutil(a,tree,mid+1,end,2*index+2);
int max2=i.max1+j.max1;
if(max2> i.sum&& max2>j.sum)
{
tree[index].max1=max(i.max1,j.max1);
tree[index].sum=max2;
return tree[index];
}
else
{
if(i.sum>j.sum)
{
tree[index].max1=max(i.max1,j.max1);
tree[index].sum= i.sum;
return tree[index];
}
else
{
tree[index].max1=max(i.max1,j.max1);
tree[index].sum=j.sum;
return tree[index];
}
}
}
node* constructst(int a[],int n)
{
int size,k;
k=(int)(ceil(log2(n)));
size=2*(int)pow(2,k)+1;
node* tree=new node[size];
constructstutil(a,tree,0,n-1,0);
return tree;
}
void updatevalueutil(int a[],node tree[],int s,int e,int i,int val,int index)
{
if(i>e||i<s)
return;
if(s==e&& s== i)
{
tree[index].max1=val;
tree[index].sum=val;
return;
}
int mid=(s+e)/2;
updatevalueutil(a,tree,s,mid,i,val,2*index+1);
updatevalueutil(a,tree,mid+1,e,i,val,2*index+2);
int i1=2*index+1;
int i2=2*index+2;
int max2=tree[i1].max1+tree[i2].max1;
if(max2> tree[i1].sum && max2>tree[i2].sum)
{
tree[index].max1=max(tree[i1].max1,tree[i2].max1);
tree[index].sum=max2;
}
else
{
if(tree[i1].sum>tree[i2].sum)
{
tree[index].max1=max(tree[i1].max1,tree[i2].max1);
tree[index].sum= tree[i2].sum;
}
else
{
tree[index].max1=max(tree[i1].max1,tree[i2].max1);
tree[index].sum=tree[i2].sum;
}
}
}
void updatevalue(int a[],int n,node tree[],int i,int val)
{
a[i]=val;
updatevalueutil(a,tree,0,n-1,i,val,0);
}
node queryutil(int a[],node tree[],int qs,int qe,int s,int e,int index)
{
node t;
t.max1=t.sum=0;
if(qs<=s&&qe>=e)
return tree[index];
if(qs>e || qe<s || qs>qe)
return t ;
int mid=(s+e)/2;
node i=queryutil(a,tree,qs,qe,s,mid,2*index+1);
node j=queryutil(a,tree,qs,qe,mid+1,e,2*index+2);
int max2=i.max1+j.max1;
if(max2> i.sum&& max2>j.sum)
{
t.sum=max2;
t.max1=max(i.max1,j.max1);
return t;
}
else
{
if(i.sum>j.sum)
{
t.sum= i.sum;
t.max1=max(i.max1,j.max1);
return t;
}
else
{
t.sum=j.sum;
t.max1=max(i.max1,j.max1);
return t;
}
}
}
long long int query(int a[],int n,node tree[],int qs,int qe)
{
int s=0;
int e=n-1;
node t= queryutil(a,tree,qs,qe,s,e,0);
return t.sum;
}
int main()
{
int n;
scanf("%d",&n);
int a[n];
for(int i=0;i<n;i++)
{
scanf("%d",&a[i]);
}
node* tree=constructst(a,n);
int k;
scanf("%d",&k);
while(k--)
{
char ch;
int index,val;
int qs,qe,ans;
cin>>ch;
if(ch=='U')
{
scanf("%d %d",&index,&val);
updatevalue(a,n,tree,index-1,val);
}
else if (ch=='Q')
{
scanf("%d %d",&qs,&qe);
long long int ans=query(a,n,tree,qs-1,qe-1);
printf("%lld\n",ans);
}
}
}