Shared code

#include <bits/stdc++.h>
using namespace std;

#define int long long

struct Node{
    int sum;
    Node(){
        sum = 0;
    }
};

vector<Node> tree(8e5);
vector<int> arr;
Node def;
int n;

Node merge(Node a, Node b){
    Node t;
    t.sum = a.sum + b.sum;
    return t;
}

void build(int index, int start, int end){
    if(start == end){
        tree[index].sum = arr[start];
        return;
    }
    int mid = (start + end)/2, left = 2*index, right = 2*index + 1;
    build(left, start, mid);
    build(right, mid+1, end);
    tree[index] = merge(tree[left], tree[right]);
}

Node update(int index, int start, int end, int pos, int val){
    if(start == end){
        tree[index].sum = val;
        return tree[index];
    }
    int mid = (start + end)/2, left = 2*index, right = 2*index + 1;
    if(mid >= pos) tree[index] = update(left, start, mid, pos, val);
    else tree[index] = update(right, mid+1, end, pos, val);
    tree[index] = merge(tree[left], tree[right]);
    return tree[index];
}

Node query(int index, int start, int end, int l, int r){
    if(start == l && end == r) return tree[index];
    else if(l > r) return def;
    int mid = (start + end)/2, left = 2*index, right = 2*index + 1;
    return merge(query(left, start, mid, l, min(r, mid)), query(right, mid+1, end, max(l, mid+1), r));
}

signed main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int q;
    cin>>n>>q;
    for(int i = 0; i < n; i++){
        int num;
        cin>>num;
        arr.push_back(num);
    }
    def.sum = 0;
    build(1,0,n-1);
    while(q--){
        int p,a,b;
        cin>>p>>a>>b;
        if(p == 1) update(1,0,n-1,a-1,b);
        else cout<<query(1,0,n-1,a-1,b-1).sum<<endl;
    }
    return 0;
}