自定義C++ Array類以支持高效的區間查詢

#include <vector>
#include <iostream>

class Array {
public:
    Array(const std::vector<int>& nums) {
        data = nums;
        buildSegmentTree(0, data.size() - 1, 0);
    }

    int query(int start, int end) {
        return queryHelper(start, end, 0, data.size() - 1, 0);
    }

private:
    std::vector<int> data;
    std::vector<int> segmentTree;

    void buildSegmentTree(int start, int end, int index) {
        if (start == end) {
            segmentTree[index] = data[start];
            return;
        }

        int mid = start + (end - start) / 2;
        buildSegmentTree(start, mid, 2 * index + 1);
        buildSegmentTree(mid + 1, end, 2 * index + 2);

        segmentTree[index] = segmentTree[2 * index + 1] + segmentTree[2 * index + 2];
    }

    int queryHelper(int queryStart, int queryEnd, int start, int end, int index) {
        if (queryStart <= start && queryEnd >= end) {
            return segmentTree[index];
        }

        if (queryStart > end || queryEnd < start) {
            return 0;
        }

        int mid = start + (end - start) / 2;
        return queryHelper(queryStart, queryEnd, start, mid, 2 * index + 1) +
               queryHelper(queryStart, queryEnd, mid + 1, end, 2 * index + 2);
    }
};

int main() {
    std::vector<int> nums = {1, 2, 3, 4, 5, 6, 7};
    Array arr(nums);

    int sum = arr.query(1, 4);
    std::cout << sum << std::endl;

    return 0;
}