non-recursive segment tree

#include<bits/stdc++.h>

#define INF 1000010000
#define nl '\n'
#define pb push_back
#define ppb pop_back
#define mp make_pair
#define fi first
#define se second
#define pii pair<int,int>
#define pdd pair<double,double>
#define all(c) (c).begin(), (c).end()
#define SORT(c) sort(all(c))
#define sz(c) (c).size()
#define rep(i,n) for( int i = 0; i < n; ++i )
#define repi(i,n) for( int i = 1 ; i <= n; ++i )
#define repn(i,n) for( int i = n - 1 ; i >= 0 ; --i )
#define repf(j,i,n) for( int j = i ; j < n ; ++j )
#define die(s) {std::cout << s << nl;}
#define dier(s) {std::cout << s; return 0;}
#define vi vector<int>
typedef long long ll;
#define MAXN 1E5 + 10
using namespace std;

int n;

vi t(2 * MAXN , 0);

void build(){
    for(int i = n - 1 ; i > 0 ; --i){
        t[i] = t[2 * i] + t[2 * i + 1];
    }
}

void modify(int p , int val){
    for(t[p += n] = val ; p > 1 ; p /= 2){
        t[p / 2] = t[p] + t[p ^ 1];
    }
}

int sum(int l , int r){//[l , r)
    int res = 0;
    for(l += n , r += n ; l < r ; l /= 2 , r /= 2){
        if(l % 2){
            res += t[l];
            ++l;
        }
        if(r % 2){
            --r;
            res += t[r];
        }
    }
    return res;
}


int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.precision(0);
    cin >> n;
    rep(i , n){
        cin >> t[n + i];
    }
    build();
    int q;
    cin >> q;
    rep(i , q){
        char type;
        cin >> type;
        if(type == 'M'){
            int el , val;
            cin >> el >> val;
            --el;
            modify(el , val);
        }else{
            int l , r;
            cin >> l >> r;
            --l , --r;
            cout << sum(l , r) << nl;
        }
    }
    return 0;
}