issues

mergesort.cpp

int acc[NMAX];

void merge(int low, int mid, int high){
    // one block from [low --> mid] and one from [mid + 1 --> high]
    // sizes (mid - low + 1), and (high - mid)
    // this one actually changes their places on the original array

    vector<long long> lower(acc + low, acc + mid + 1);
    vector<long long> higher(acc + mid + 1, acc + high + 1);

    int i = 0; // for lower
    int j = 0; // for higher

    for (int index = low; index <= high; index++){
        if (lower[i] <= higher[j]){
            acc[index] = lower[i];
            i++;
        }
        else {
            acc[index] = higher[j];
            j++;
        }
    }
}


void mergesort(int low, int high){
    // pass indexes to the array acc in, and merge sort those sections
    // thses are inclusive array indices
    if(low >= high){
        return;
    }

    int mid = (low + high)/2;
    mergesort(low, mid);
    mergesort(mid + 1, high);
    merge(low, mid, high);
}