Quick Sort (Optimized + Insertion Sort) - Ruby

#! /usr/bin/env ruby

# str is array of chars
# pivot point is index in array to pivot on
# returns type like `str`
#! /usr/bin/env ruby
def sorted?(arr)
    for i in 1...arr.length
        return false if arr[i] < arr[i-1]
    end

    return true
end

def insertionsort(str)
    strlen = str.length
    while !sorted?(str)

        for i in 1...strlen #exclusive range

            if str[i-1] > str[i]
                hold = str[i] # store value to INSERT

                pos = i

                while pos > 0 && str[pos - 1] > hold
                    str[pos] = str[pos - 1] # shift up
                    pos -= 1

                    # stop if we have shifted all the elements that are BOTH greater than str[i] AND
                    # to the left of str[i]
                end

                # put str[i] in its rightful spot, just left of the last element we shifted, or the original spot of
                # the last element we shifted
                str[pos] = hold
            end

        end
    end

    return str
end

def quicksort(str, _begin, _end)
    return str[_begin..._end] if _end - _begin <= 1

    if _end - _begin <= 10
        return insertionsort(str[_begin..._end])
    end


    pivot = str[_end - 1] # choose last as pivot

    a = _begin
    b = _end - 1

    while (b > a)
        if str[b-1] > pivot
            str[b] = str[b-1]
            b-=1
        else
            str[b-1],str[a] = str[a],str[b-1]
            a+=1
        end
    end

    str[b] = pivot

    str[ _begin...b ] = quicksort(str, _begin, b) if b - _begin > 1
    str[ (b+1)..._end] = quicksort(str, b+1, _end) if _end - b > 1

    return str[_begin..._end]

end

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

puts quicksort(str, 0, str.length).join('')