Given a function that generates perfectly random numbers between 1 and k (inclusive), where k is an input, write a function that shuffles a deck of cards represented as an array using only swaps. It should run in O(N) time. Hint: Make sure each one of the 52! permutations of the deck is equally likely.

daily-coding-problem-51.rb

#!/usr/bin/env ruby

def deck
    ranks = ['A',*(2..10),'J','Q','K']
    suits = ['♠','♦','♣','♥'] 
    deck = [] 
    suits.product(ranks).map { |rank, suit| deck << "#{rank}#{suit}" }
    deck
end

def shuffle deck 
    deck.each_with_index do |card, i|
        rnd = i + rand(deck.size()-i)
        deck[i], deck[rnd] = deck[rnd], deck[i]
    end 
    return deck
end

p shuffle(deck).pop(5)

K is input, you can not consider the deck size as input to the rand function.

@CristianoPassos could you please elaborate?

I wrote this quite some time ago. I understood the question as k is the length of the deck. Ruby has a random number generator rand() built into its standard library. So I just chose to use that. Is there something I am missing here?

I understand my code may not run in the O(N) time complexity. At the time I wrote this, I had next to no experience in optimization, and Big O(N) notation.