[冬令营Day1 T2]sequence

#include<iostream>
#include<cmath>
#include<cstring>
#include<cstdio>
#include<algorithm>
#include<queue>
using namespace std;
typedef long long LL;
inline int read()
{
    int x=0,f=1;char c=getchar();
    while(!isdigit(c)){if(c==‘-‘)f=-1;c=getchar();}
    while(isdigit(c)){x=x*10+c-‘0‘;c=getchar();}
    return x*f;
}
const int oo=2147000000;
const int maxn=1000010;
int n,q,a[maxn],x,y;
LL pre[maxn],sum[maxn],suml[maxn],sumr[maxn];
void build(int l,int r,int o)
{
    if(l==r)
    {
        suml[o]=sumr[o]=sum[o]=pre[r]-pre[l-1];
        return;
    }
    int mid=(l+r)>>1,lo=o<<1,ro=lo+1;
    build(l,mid,lo);
    build(mid+1,r,ro); 
    sum[o]=max(sum[lo],sum[ro]);
    sum[o]=max(sum[o],sumr[lo]+suml[ro]);  
    suml[o]=max(suml[lo],pre[mid]-pre[l-1]+suml[ro]);  
    sumr[o]=max(sumr[ro],pre[r]-pre[mid]+sumr[lo]);
    return;  
}
LL queryl(int x,int y,int l,int r,int o)
{
    if(x==l && y==r) return sumr[o];  
    int mid=(l+r)>>1,lo=o<<1,ro=lo+1;  
    if(x>mid) return queryl(x,y,mid+1,r,ro);    
    else
    {  
        LL tmp=pre[r]-pre[mid]+queryl(x,mid,l,mid,lo);  
        return max(sumr[ro],tmp);  
    }    
}
LL queryr(int x,int y,int l,int r,int o) 
{
    if(x==l && y==r) return suml[o];  
    int mid=(l+r)>>1,lo=o<<1,ro=lo+1;  
    if(y<=mid) return queryr(x,y,l,mid,lo);  
    else
    {  
        LL tmp=pre[mid]-pre[l-1]+queryr(mid+1,y,mid+1,r,ro);  
        return max(suml[lo],tmp);  
    }  
}
LL query(int x,int y,int l,int r,int o)
{
    if(x<=l && y>=r)return sum[o];   
    int mid=(l+r)>>1,lo=o<<1,ro=lo+1;  
    if(y<=mid) return query(x,y,l,mid,lo);  
    else if(x>mid) return query(x,y,mid+1,r,ro);  
    else 
    {  
        LL ls,rs;  
        ls=queryl(x,mid,l,mid,lo);  
        rs=queryr(mid+1,y,mid+1,r,ro);  
        return max(max(query(x,mid,l,mid,lo),query(mid+1,y,mid+1,r,ro)),rs+ls);  
    }  
}
int main()
{
    freopen("sequence.in","r",stdin);
    freopen("sequence.out","w",stdout);
    n=read();q=read();
    for(int i=1;i<=n;i++)a[i]=read(),pre[i]=pre[i-1]+a[i];
    build(1,n,1);
    while(q--)
    {
        x=read();y=read();
        LL tmp=query(x,y,1,n,1);
        if(tmp<0)tmp=0;
        printf("%lld\n",tmp);
    }
    return 0;
}