About sort method

Question

I want to know why following 2 ways to use sort method can reverse the elements in the array "a".

a = (1..100).to_a
(1)
a2 = a.sort{|n1, n2| n2 <=> n1 }
p a2

(2)
a3 = a.sort_by{|i| -i }
p a3

Thank u for ur helping.

Answer 1

start with shell and bubble sort algoritms