9pts求助

#include<iostream>
#define int long long
using namespace std;
struct node{
    int mal, mar, sum, ans;
}T[500005 << 2];
int a[500005];
int n, m;
inline int ls(int p) {
    return p << 1;
}
inline int rs(int p) {
    return p << 1 | 1;
}
void pushup(int p) {
    T[p].sum = T[ls(p)].sum + T[rs(p)].sum;
    T[p].ans = max( max(T[ls(p)].ans, T[rs(p)].ans), T[ls(p)].mar + T[rs(p)].mal);
    T[p].mal = max(T[ls(p)].mal, T[ls(p)].sum + T[rs(p)].mal);
    T[p].mar = max(T[rs(p)].mar, T[rs(p)].sum + T[ls(p)].mar);
}
void build(int l, int r, int p) {
    if(l == r) {
        T[p].sum = a[l];
        T[p].mal = T[p].mar = T[p].ans = T[p].sum;
        return;
    }
    int mid = (l + r) >> 1;
    build(l, mid, ls(p));
    build(mid + 1, r, rs(p));
    pushup(p);
}
node query(int sl, int sr, int l, int r, int p) {
    if(sl <= l and r <= sr) 
        return T[p];
    int mid = (l + r) >> 1;
    if(sl <= mid) 
        return query(sl, sr, l, mid, ls(p));
    else {
        if(mid < sr) 
            return query(sl, sr, mid + 1, r, rs(p));
        else {
            node q, ll = query(sl, sr, l, mid, ls(p)), rr = query(sl, sr, mid + 1, r, rs(p));
            q.mal = max(ll.mal, ll.sum + rr.mal);
            q.mar = max(rr.mar, rr.sum + ll.mar);
            q.ans = max( max(ll.ans, rr.ans), ll.mar + rr.mal);
            return q;
        }
    }
}
void update(int sl, int l, int r, int p, int k) {
    if(l == r) {
        T[p].mal = T[p].mar = T[p].ans = T[p].sum = k;
        return;
    }
    int mid = (l + r) >> 1;
    if(mid >= sl)
        update(sl, l, mid, ls(p), k);
    else 
        update(sl, mid + 1, r, rs(p), k);
    pushup(p);
}
signed main() {
    std::ios::sync_with_stdio(0);
    cin>>n>>m;
    for(int i = 1; i <= n; i++)
        cin>>a[i];
    build(1, n, 1);
    int op, x, y;
    while(m--) {
        cin>>op>>x>>y;
        if(op == 1) {
            if(x > y) 
                swap(x, y);
            cout<<query(x, y, 1, n, 1).ans<<'\n';
        }
        else 
            update(x, 1, n, 1, y);
    }
    return 0;
}