Slide 13
Slide 13 text
ۙگ
$ irb
irb(main):001:0> (1..9).to_a
=> [1, 2, 3, 4, 5, 6, 7, 8, 9]
irb(main):002:0> (1..9).to_a.repeated_combination(2).to_a
=> [[1, 1], [1, 2], [1, 3], [1, 4], [1, 5], [1, 6], [1, 7], [1,
8], [1, 9], [2, 2], [2, 3], [2, 4], [2, 5], [2, 6], [2, 7], [2,
8], [2, 9], [3, 3], [3, 4], [3, 5], [3, 6], [3, 7], [3, 8], [3,
9], [4, 4], [4, 5], [4, 6], [4, 7], [4, 8], [4, 9], [5, 5], [5,
6], [5, 7], [5, 8], [5, 9], [6, 6], [6, 7], [6, 8], [6, 9], [7,
7], [7, 8], [7, 9], [8, 8], [8, 9], [9, 9]]
irb(main):003:0> (1..9).to_a.repeated_combination(2).collect{|a|
a[0]*a[1]}
=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 4, 6, 8, 10, 12, 14, 16, 18, 9, 12,
15, 18, 21, 24, 27, 16, 20, 24, 28, 32, 36, 25, 30, 35, 40, 45,
36, 42, 48, 54, 49, 56, 63, 64, 72, 81]
irb(main):004:0> (1..9).to_a.repeated_combination(2).collect{|a|
a[0]*a[1]}.uniq.size
=> 36
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