9ptsWA,玄关，求调（码风比较正常）

#include <bits/stdc++.h>
using namespace std;
#define int long long
const int N = 6 * 1e6, MIN = -1e9;
struct nm
{
    int sum, lmax, rmax, rt;
}num[N];
int n, q;
int a[N];
inline int read()
{
    char c;
    int sign = 1;
    while((c = getchar()) > '9' || c < '0')
    {
        if(c == '-')
            sign = -1;
    }
    int res = c - '0';
    while((c = getchar()) >= '0' && c <= '9')
        res = res * 10 + c - '0';
    return res * sign;
}
void update(int u)
{
    num[u].lmax = max(num[u << 1].lmax, num[u << 1].sum + num[u << 1 | 1].lmax);
    num[u].rmax = max(num[u << 1 | 1].rmax, num[u << 1 | 1].sum + num[u << 1].rmax);
    num[u].sum = num[u << 1].sum + num[u << 1 | 1].sum;
    num[u].rt = max(num[u << 1].rt, num[u << 1 | 1].rt);
    num[u].rt = max(num[u].rt, num[u << 1].rmax + num[u << 1 | 1].lmax);
}
void build(int u, int l, int r)
{
    if(l == r)
    {
        num[u].sum = num[u].lmax = num[u].rmax = num[u].rt = a[l];
        return;
    }
    int mid = l + r >> 1;
    build(u << 1, l, mid);
    build(u << 1 | 1, mid + 1, r);
    update(u);
}
nm query(int u, int l, int r, int x, int y)
{
    if(l >= x && r <= y) return num[u];
    //if(l > y || r < x) return MIN;
    int mid = l + r >> 1;
    nm ret;
    if(mid >= y) return query(u << 1, l, mid, x, y);
    if(mid + 1 <= x) return query(u << 1 | 1, mid + 1, r, x, y);
    nm ls = query(u << 1, l, mid, x, y);
    nm rs = query(u << 1 | 1, mid + 1, r, x, y);
    ret.sum = ls.sum + rs.sum;
    ret.lmax = max(ls.lmax, ls.sum + rs.lmax);
    ret.rmax = max(rs.rmax, rs.sum + ls.rmax);
    ret.rt = max(ret.lmax, ret.rmax);
    ret.rt = max(ret.rt, ls.rmax + rs.lmax);
    return ret;
}
void ch(int u, int l, int r, int x, int y)
{
    if(l == r && l == x)
    {
        num[u].sum = num[u].lmax = num[u].rmax = num[u].rt = y;
        return;
    }
    int mid = l + r >> 1;
    if(x <= mid) ch(u << 1, l, mid, x, y);
    else ch(u << 1 | 1, mid + 1, r, x, y);
    update(u);
}
signed main()
{
    //freopen("P4513_2.in", "r", stdin); 
    n = read();
    q = read();
    for(int i = 1; i <= n; i++) a[i] = read();

    //memset(lmax, -0x3f3f3f, szieof)
    build(1, 1, n); 
    for(int i = 1; i <= q; i++)
    {
        int opt = read();
        int x = read(), y = read();
        if(opt == 2) ch(1, 1, n, x, y);
        if(opt == 1) 
        {
            if(x > y) swap(x, y);
            cout << query(1, 1, n, x, y).rt << endl;
        }
    }
    return 0;
}