2042 구간 합 구하기

펜윅트리 사용해서 풀었는데 아직 펜윅트리가 낯설다,,, 

#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
#include <functional>
#include <string>
#include <queue>
#include <deque>
#include <stack>
#include <set>
#include <map>
#include <cmath>
#include <cstring>
#include <bitset>

#define xx first
#define yy second
#define all(x) (x).begin(), (x).end()

using namespace std;
using i64 = long long int;
using ii = pair<int, int>;
using iis = pair<int, string>;
using ii64 = pair<i64, i64>;
using iii = tuple<int, int, int>;

i64 sum(vector<i64> &tree, int i) {
    i64 ans = 0;
    
    while (i > 0) {
        ans += tree[i];
        i -= (i & -i);
    }
    return ans;
}

void update(vector<i64> &tree, int i, i64 diff) {
    while (i < tree.size()) {
        tree[i] += diff;
        i += (i & -i);
    }
}

int main() {
    int n, m, k;
    scanf("%d %d %d", &n, &m, &k);
    
    vector<i64> a(n + 1);
    vector<i64> tree(n + 1);
    
    for (int i = 1; i <= n; i++) {
        scanf("%lld", &a[i]);
        update(tree, i, a[i]);
    }
    
    m += k;
    int t1, t2, t3;
    i64 t4;
    while (m--) {
        scanf("%d", &t1);
        
        if (t1 == 1) {
            scanf("%d %lld", &t2, &t4);
            i64 diff = t4 - a[t2];
            
            a[t2] = t4;
            update(tree, t2, diff);
        } else {
            int t2, t3;
            
            scanf("%d %d", &t2, &t3);
            printf("%lld\n", sum(tree, t3) - sum(tree, t2 - 1));
        }
    }
    
    return 0;
}