function partition(v::Vector{T}, from::Int, to::Int)::Int where {T}
    piv = v[to]
    i = from-1
    for j = from:to-1
        if v[j] <= piv
            i += 1
            v[i], v[j] = v[j], v[i]
        end
    end
    i += 1
    v[i], v[to] = v[to], v[i]
    i
end

function hoare!(v::AbstractArray, from::Int, to::Int)::Int
    if from >= to
        return from
    end
    lo, hi = from-1, to+1
    piv = v[div(from+to,2)]
    while true
        lo += 1
        while v[lo] < piv
            lo += 1
        end
        hi -= 1
        while v[hi] > piv
            hi -= 1
        end
        if lo >= hi
            return hi
        end
        v[lo], v[hi] = v[hi], v[lo]
    end
end

function quicksort!(v::Vector{T}, from=1, to=-1) where {T}
    if to < 0
        to = length(v)
    end
    if to <= from
        return
    else
        mid = hoare!(v, from, to)
        quicksort!(v, from, mid)
        quicksort!(v, mid+1, to)
    end
end