震惊！本地下载数据全部对拍AC，咕测全WA，网友：怎么可能！？

rt

#include <bits/stdc++.h>
#define ls(x) x << 1
#define rs(x) x << 1|1
#define inf 0x3f3f3f3f

using namespace std;
const int N = 5e5 + 10; 

int n , m , a[N];

struct Seg {
    int l , r , len;
    int lft , rgt , mid , dis;
}t[N << 2];

void pushup(int x) {
    t[x].dis = t[ls(x)].dis + t[rs(x)].dis;
    t[x].lft = max(t[ls(x)].lft , t[ls(x)].dis + t[rs(x)].lft);
    t[x].rgt = max(t[rs(x)].rgt , t[rs(x)].dis + t[ls(x)].rgt);
    t[x].mid = max(t[ls(x)].mid , t[rs(x)].mid);
    t[x].mid = max(t[x].mid , t[ls(x)].rgt + t[rs(x)].lft);
}

void built(int x  , int l ,int r ) {
    t[x].l = l , t[x].r = r;
    t[x].len = r - l + 1;
    if(l == r) {
        t[x].lft = t[x].rgt = t[x].mid = t[x].dis = a[l]; return;
    }
    int mid = (l + r )>> 1;
    built(ls(x) , l , mid);
    built(rs(x) , mid + 1 , r);
    pushup(x);
}

Seg query(int x , int l , int r ) {
    if(t[x].l >= l && t[x].r <= r) return t[x];
    int mid = (t[x].l + t[x].r) >> 1;
    Seg ans , lson , rson;
    lson.dis = lson.mid = lson.lft = lson.rgt = -inf;
    rson.dis = rson.mid = rson.lft = rson.rgt = -inf;
    if(l <= mid) lson = query(ls(x) , l , r);
    if(r > mid ) rson = query(rs(x) , l , r);
    ans.lft = max(lson.lft , rson.lft + lson.dis);
    ans.rgt = max(rson.rgt , lson.rgt + rson.dis);
    ans.mid = max(lson.mid , rson.mid);
    ans.mid = max(ans.mid , lson.rgt + rson.lft);
    pushup(x);
    return ans;
}

void updata(int x , int p , int w) {
    if(t[x].l == t[x].r) {
         t[x].lft = t[x].rgt = t[x].mid = t[x].dis = w; return;
    }
    int mid = (t[x].l + t[x].r) >> 1;
    if(p <= mid) updata(ls(x) , p , w);
    else updata(rs(x) , p , w);
    pushup(x);
}

int main () {
    //freopen("data.txt" , "r" , stdin);
    //freopen("ans1.out" , "w" , stdout);
    scanf("%d %d" , &n, &m);
    for(int i = 1 ; i <= n ; ++ i) scanf("%d" , a + i);
    built(1 ,1  ,n);
    while( m --) {
        int opt , l , r;
        scanf("%d %d %d" , &opt , &l , &r);
        if(opt == 1) {
            if(l > r) swap(l , r); 
            Seg rans = query(1 , l , r);
            printf("%d\n" , rans.mid);
        } else {
            updata(1 , l , r);
        }
    }
    return 0;
}