Quick Sort - Ruby

#! /usr/bin/env ruby

# str is array of chars
# pivot point is index in array to pivot on
# returns type like `str`
def quicksort(str, pivot_point)
    strlen = str.length

    # recursion terminating condition:
    return str if strlen <= 1

    # find the pivot character
    pivot_char = str[pivot_point]

    # make new arrays for left and right of pivot
    # note: I'm very much aware that this is not the most efficient method,
    # but it WILL make it easier to understand the concept of quicksort before
    # I proceed to cover the in-place version
    left = []
    right = []

    # go through all the elements, put the ones smaller than pivot_char on the left;
    # ...bigger on the right.
    for i in 0...strlen # exclusive range: 0 to one less than str's length
        next if i == pivot_point # skip over the pivot, we don't want to put it anywhere
        # because it'll already be in final position at the end of the function.

        if str[i] < pivot_char
            left << str[i]
        else
            right << str[i]
        end
    end

    # utilize recursion to sort the left and right arrays, until the partitions become
    # a singular-element array or an empty one.
    left = quicksort(left, rand(left.length))
    right = quicksort(right, rand(right.length))

    # overwrite the original str and drop the new stuff in, in order
    str = []
    str << left << pivot_char << right

    return str.flatten # flatten because we pushed an array, a character/one-letter-string, and another array
    # FYI: flatten makes a 2+D array 1D.

end

puts "give me a string"
str = gets.chomp.split('')

puts quicksort(str, rand(str.length)).join('')