누적합? -> 펜윅트리를 사용해보자!
펜윅트리!
#include<bits/stdc++.h>
using namespace std;
#define MAX 100010
int arr[MAX];
int n;
void input(int idx, int num) {
while (idx <= n + 1) {
arr[idx] += num;
idx += (idx & -idx);
}
}
int sum(int idx) {
int _sum = 0;
while (idx) {
_sum += arr[idx];
idx -= (idx & -idx);
}
return _sum;
}
int main() {
ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
cin >> n;
for (int i = 1; i <= n; i++) {
int num; cin >> num;
input(i, num);
}
int m; cin >> m;
while (m--) {
int i, j; cin >> i >> j;
cout << sum(j) - sum(i - 1) << '\n';
}
return 0;
}