If I randomly guess a number between 1 & 1000, when will the numbers collide?

collision.rb

def detect_collision(number)
  guessed_numbers = {}
  count = 0
  collision = false

  while !collision
    guess = rand(number)
    count += 1

    if guessed_numbers[guess]
      collision = true
    end

    guessed_numbers[guess] = true
  end

  count
end

tries = 100

results = (1..tries).to_a.map do |i|
  detect_collision(1_000)
end

puts results

sum = results.inject(0) { |memo, i| memo + i }

puts "Average: #{sum / tries}"


# ...
# 56
# 31
# 40
# 78
# 23
# 42
# 73
# 62
# 49
# 29
# Average: 39