Seg tree build update query(max)

#include "bits/stdc++.h"
using namespace std;
const int N = 1e4;
typedef long long int ll;
ll arr[N], tree[N];

void build(int l, int r, int idx){
    if(l == r){
        tree[idx] = arr[l];
        return;
    }
    ll mid = l + r >> 1;
    build(1, mid, 2 * idx);
    build(mid + 1, r, 2* idx + 1);

    tree[idx] = max(tree[2 * idx], tree[2 * idx + 1]);
}
void update(int l, int r, int pos, ll val, int idx){
     if(l == r && pos == l){
        tree[idx] = val;
          return ;
    }
    if(l > pos || pos > r)return;

    ll mid = (l + r) >> 1;

    update(l, mid, pos, val, 2 * idx);
    update(mid + 1, r, pos, val, 2 * idx + 1);
    tree[idx] = max(tree[2 * idx], tree[2 * idx + 1]);


}
ll query(int l, int r, int ql, int qr, int idx){
    if(ql > r || qr < l)return 0;
    if(ql <= l && r <= qr)return tree[idx];
    ll mid = l + r >> 1;
    ll x = query(l, mid, ql, qr, 2 * idx);
    ll y = query(mid + 1, r, ql , qr, 2 * idx + 1);
    return max(x, y);
}
int main(){
    int i, n, q;
    cin >> n >> q;
    for(i = 1; i <= n; i++)
    cin >> arr[i];

    build(1, n, 1);
    cout << tree[1] << endl;
    update(1, n, 2, 100, 1);
    cout << tree[1] << endl;
    while(q--){
        int x, y;
        cin >> x >> y;
        cout << query(1, n, x, y, 1) << endl;
    }
    return 0;
}