Merge sort

void merger(vector<int>& T, int l, int m, int r)
{
    vector<int> L(T.begin() + l, T.begin() + m + 1),
                R(T.begin() + m + 1, T.begin() + r + 1);
    L.push_back(INT_MAX), R.push_back(INT_MAX);

    for (int li = 0, ri = 0; li < L.size() - 1 || ri < R.size() - 1;)
        T[l + li + ri - 1] = (L[li] <= R[ri] ? L[li++] : R[ri++]);
}

void merge_sort(std::vector<int>& T, int l, int r)
{
    if (l < r)
    {
        int m = l + (r - l) / 2;
        merge_sort(T, l, m), merge_sort(T, m + 1, r);
        merger(T, l, m, r);
    }
}