Official Solution

Time Complexity: $O((N+Q\log N)\log N)$

Memory Complexity: $O(N\log N)$

Alternative Solution 1 (Persistent Segment Tree)

The factor of $Q\log^2N$ from the solution above can be reduced to $Q\log N$ by replacing binary search with a segment tree walk.

Alternative Solution 2 (Wavelet Tree)

Similar as the Wavelet tree module problem. All you need to change is the recursive query step.

Time Complexity: $O(N+Q\log N)$

Memory Complexity: $O(N)$

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

 Code Snippet: BitVector Prefix Summer (Click to expand)

int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);

	int N, Q;