algorithm/merge_sort.cpp at main · ihbadhon/algorithm · GitHub

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void merge(vector<int>& arr, int left, int mid, int right) {
 // cout << left << " " << right << endl;
    int n1 = mid - left + 1;
    int n2 = right - mid;

    vector<int> L(n1);
    vector<int> R(n2);

    for (int i = 0; i < n1; i++)
        L[i] = arr[left + i];

    for (int i = 0; i < n2; i++)
        R[i] = arr[mid + 1 + i];

    int i = 0, j = 0, k = left;

    while (i < n1 && j < n2) {
        if (L[i] <= R[j]) {
            arr[k] = L[i];
            i++;
        } else {
            arr[k] = R[j];
            j++;
        }
        k++;
    }

    while (i < n1) {
        arr[k] = L[i];
        i++;
        k++;
    }

    while (j < n2) {
        arr[k] = R[j];
        j++;
        k++;
    }
}

void mergeSort(vector<int>& arr, int left, int right) {
    if (left < right) {
        int mid = left + (right - left) / 2;
        mergeSort(arr, left, mid);
        mergeSort(arr, mid + 1, right);
        merge(arr, left, mid, right);
    }
}

//................................................................................................................
//// End ......................................................................................................................................................


///// another implementation
vector<int> arr(M);
vector<int> v(M);

void merging(int left, int mid, int right)
{
    int first, second, i;
    first = left;
    second = mid + 1;

    for(i = first; first<=mid and second<=right; i++)
    {
        if(v[first]<v[second])
            arr[i] = v[first++];
        else
            arr[i] = v[second++];
    }


    while(first<=mid)
        arr[i++] = v[first++];
    while(second<=right)
        arr[i++] = v[second++];

    for(i=left; i<=right; i++)
        v[i] = arr[i];

}


void sorting(int left, int right)
{
    if(left>=right) return ;
    int mid = (left + right)/2;

    sorting(left, mid);
    sorting(mid+1, right);

    merging(left, mid, right);
}