Partition(a, m, p)
    v = a[m]
    i = m
    j = p
    repeat
        repeat
            i = i + 1
        until a[i] > v
        repeat
            j = j - 1
        until a[j] < v
        if i < j then
            Interchange(a, i, j)
    until i > j
    a[m] = a[j]
    a[j] = v
    return j


Interchange(a, i, j)
    temp = a[i]
    a[i] = a[j]
    a[j] = temp


QuickSort(a, p, q)
    if p < q then
        j = Partition(a, p, q + 1)
        QuickSort(a, p, j - 1)
        QuickSort(a, j + 1, q)