vector.push_back不会导致正确的值被推回

Question

我正在练习合并排序（用于面试准备）。我遇到了一个非常奇怪的向量问题。似乎将某个值推回到向量上并不会导致该值实际放在那里。我可能会遗漏一些明显的东西，但我不确定。以下是合并排序的代码（添加了一些打印语句以了解出现了什么问题）

void merge(std::vector<int> *vec, int low, int middle, int high) {
    printf("Entering Merge(%d, %d, %d)\n", low, middle, high);
    std::vector<int> helper;
    for(int i = low; i <= high; ++i) {
        helper.push_back( (*vec)[i] );
    }
    std::cout << "Array being worked on: [";
    for(auto &p : helper) {
        std::cout << p << ", ";
    } std::cout << "]" << std::endl;

    int helperLeft = low, helperRight = middle + 1, vecIndex = low;
    while(helperLeft <= middle && helperRight <= high) {
        if(helper[helperLeft] <= helper[helperRight]) {
            (*vec)[vecIndex] = helper[helperLeft];
            ++helperLeft;
            std::cout << "Helper Left: " << helperLeft << std::endl; 
        }
        else {
            (*vec)[vecIndex] = helper[helperRight];
            ++helperRight;
            std::cout << "Helper Right: " << helperRight << std::endl;
        }
        ++vecIndex;
        std::cout << "Current Index: " << vecIndex   << std::endl;
    }

    // Copy over the remaining elements into the array
    while(helperLeft <= middle) {
        std::cout << "Entered Left Remaining" << std::endl;
        (*vec)[vecIndex] = helper[helperLeft];
        ++helperLeft;
        ++vecIndex;
    }

    while(helperRight <= high) {
        std::cout << "Entered Right Remaining" << std::endl;
        (*vec)[vecIndex] = helper[helperRight];
        ++helperRight;
        ++vecIndex;
    }
    std::cout << "Resulting Array: [";
    for(int i = low; i < high; ++i) {
        std::cout << (*vec)[i] << ", ";
    } std::cout << (*vec)[high] << "]" << std::endl;
    std::cout << std::endl;
}

void mergeSort(std::vector<int> *vec, int low, int high) {
    if(low < high) {
        int middle = (low + high) / 2;
        mergeSort(vec, low, middle);
        mergeSort(vec, middle + 1, high);
        merge(vec, low, middle, high);
    }
}

int main() {
    std::vector<int> array({2, 25, 1, 1, 5});
    mergeSort(&array, 0, array.size() - 1);
}