在C++中查找向量中每个索引处累积的唯一元素计数的有效方法

#include <iostream>
#include <vector>
#include <unordered_map>

std::vector<int> countUniqueElements(const std::vector<int>& nums) {
    std::unordered_map<int, int> counts;
    std::vector<int> result;

    for (int num : nums) {
        if (counts.find(num) == counts.end()) {
            counts[num] = 1;
        } else {
            counts[num]++;
        }
    }

    for (int i = 0; i < nums.size(); i++) {
        result.push_back(counts[nums[i]]);
    }

    return result;
}

int main() {
    std::vector<int> nums = {1, 2, 3, 2, 1, 3, 4, 5};
    std::vector<int> result = countUniqueElements(nums);

    for (int count : result) {
        std::cout << count << " ";
    }
    std::cout << std::endl;

    return 0;
}