调完bug后，我的程序终于9分了，求查错

#include<iostream>
#include<cstring>
#include<cstdio>
#include<algorithm>
#include<queue>
#include<cmath>
#include<vector>
#define maxn 500005
#define rint register int
#define ll long long
#define inf 0x3f3f3f3f
#define pb push_back
#define mod (int)1e9 + 7
using namespace std;
inline int read()
{
    char c=getchar();int x=0,f=1;
    while(c<'0'||c>'9'){if(c=='-')f=-1;c=getchar();}
    while(c>='0'&&c<='9'){x=x*10+c-'0';c=getchar();}
    return x*f;
}
inline void write(int x)
{
    if(x<0) putchar('-'),x=-x;
    if(x>9) write(x/10);
    putchar(x%10+'0');
    return ;
}

struct SegmentTree
{
    int l, r, sum, lmax, rmax, dat;
    #define l(x) tree[x].l
    #define r(x) tree[x].r
    #define lm(x) tree[x].lmax
    #define rm(x) tree[x].rmax
    #define sum(x) tree[x].sum
    #define dat(x) tree[x].dat 
} tree[maxn*4];
int a[maxn], n, m;

inline void update (int p)
{
    //cout<<"update"<<endl;
    sum(p) = sum(p*2) + sum(p*2+1);
    lm(p) = max(lm(p*2), sum(p*2) + lm(p*2+1));
    rm(p) = max(rm(p*2+1), sum(p*2+1) + rm(p*2));
    dat(p) = max(dat(p*2), max(dat(p*2+1), lm(p*2+1) + rm(p*2)));
}

inline void build (int p, int l, int r)
{
    //cout<<"build"<<endl;
    l(p)=l, r(p)=r;
    if (l==r) { lm(p) = rm(m) = sum(p) = dat(p) = a[l]; return; }
    int mid = (l(p)+r(p)) >> 1;
    build (p*2, l, mid);
    build (p*2+1, mid+1, r);
    update(p);
}

void change (int p, int pos, int d)
{
    //cout<<"change"<<endl;
    if (l(p) == r(p))
    {
        lm(p) = rm(m) = sum(p) = dat(p) = d;
        return; 
    }
    int mid = (l(p)+r(p)) >> 1;
    if (pos <= mid) change(p*2, pos, d);
    else change(p*2+1, pos, d);
    update(p);
} 

SegmentTree query (int p, int l, int r)
{
    //cout<<"query"<<endl;
    if (l<=l(p) && r>=r(p)) return tree[p];
    int mid = (l(p)+r(p)) >> 1;
    if (r <= mid) return query(p*2, l, r);
    else if (l > mid) return query(p*2+1, l, r);
    else
    {
        SegmentTree x=query(p*2, l, r), y=query(p*2+1, l, r), res;
        res.sum = x.sum + y.sum;
        res.lmax = max(x.sum + y.lmax, x.lmax);
        res.rmax = max(y.sum + x.rmax, y.rmax);
        res.dat = max( max(x.dat, y.dat), x.rmax + y.lmax);
        return res;
    }
}

int main()
{
    n=read(), m=read();
    for (rint i=1; i<=n; ++i) a[i]=read();
    build (1, 1, n);
    while (m--)
    {
        int op = read();
        int x=read(), y=read();
        if (op == 1)
        {
            //cout<<"op1"<<endl;
            if (x > y) swap(x, y);
            SegmentTree ans = query(1, x, y);
            write(ans.dat), puts("");
        }   
        else change(1, x, y);
    }   
    return 0;
}