Competitive Programming in Ruby (101)

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Compe&&ve Programming in Ruby (101) RubyKaigi 2016 Kyoto A1er Party LT (2016-09-10) @yhara (Yutaka Hara) RubyKaigi 2016 Kyoto LT (2016-09-10) 1

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Recently I'm trying Compe22ve Programming with my colleagues RubyKaigi 2016 Kyoto LT (2016-09-10) 3

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Compe&&ve Programming RubyKaigi 2016 Kyoto LT (2016-09-10) 4

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Programming contest RubyKaigi 2016 Kyoto LT (2016-09-10) 5

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Write a program fast and correctly RubyKaigi 2016 Kyoto LT (2016-09-10) 6

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Need C(++, #) or Java? RubyKaigi 2016 Kyoto LT (2016-09-10) 7

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You can use Ruby too! RubyKaigi 2016 Kyoto LT (2016-09-10) 8

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Sites which supports Ruby • Sphere Online Judge • Aizu Online Judge • yukicoder • AtCoder ←Today's topic RubyKaigi 2016 Kyoto LT (2016-09-10) 9

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atcoder.jp • AtCoder Grand Contest • AtCoder Regular Contest • AtCoder Beginner Contest • AtCoder Typical Contest RubyKaigi 2016 Kyoto LT (2016-09-10) 10

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Don't join the contest RubyKaigi 2016 Kyoto LT (2016-09-10) 11

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Try previous contests ﬁrst ! RubyKaigi 2016 Kyoto LT (2016-09-10) 12

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! • Any%me • No %me limit RubyKaigi 2016 Kyoto LT (2016-09-10) 13

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• AtCoder Grand Contest • AtCoder Regular Contest • AtCoder Beginner Contest • AtCoder Typical Contest RubyKaigi 2016 Kyoto LT (2016-09-10) 14

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AtCoder Beginner Contest • A: Very easy • B: Easy • C: Easy? • D: Not really easy RubyKaigi 2016 Kyoto LT (2016-09-10) 15

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But Ruby is slow...? ! RubyKaigi 2016 Kyoto LT (2016-09-10) 16

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No problem! RubyKaigi 2016 Kyoto LT (2016-09-10) 17

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Algorithm Ma-ers ! RubyKaigi 2016 Kyoto LT (2016-09-10) 18

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Example: one-line Reversi RubyKaigi 2016 Kyoto LT (2016-09-10) 19

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one-line Reversi • Given N pieces, ﬂip Q ranges • Calculate the ﬁnal state ●●●●●●●●● 1..4 2..6 8..9 ɹɹ↓ ○●●●○○●○○ RubyKaigi 2016 Kyoto LT (2016-09-10) 20

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Just ﬂipping each pieces? ranges.each do |r| r.each do |i| line[i] = !line[i] end end RubyKaigi 2016 Kyoto LT (2016-09-10) 21

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200,000 pieces ! 200,000 ranges ! RubyKaigi 2016 Kyoto LT (2016-09-10) 23

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Billions of ﬂips ! ranges.each do |r| # <- 200,000 times r.each do |i| # <- 50,000 times or so line[i] = !line[i] end end RubyKaigi 2016 Kyoto LT (2016-09-10) 24

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⏰ Time Limit = 2 sec. RubyKaigi 2016 Kyoto LT (2016-09-10) 25

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Be#er algorithm Memorize where color changes 10001 23005 ɹɹɹɹ↓ɹɹ↓ ●●●...●○...○●●● RubyKaigi 2016 Kyoto LT (2016-09-10) 26

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Passed! ! RubyKaigi 2016 Kyoto LT (2016-09-10) 27

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You can try Compe//ve Prograaming in Ruby ! (at least for beginner contest) RubyKaigi 2016 Kyoto LT (2016-09-10) 28

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! BTW ! RubyKaigi 2016 Kyoto LT (2016-09-10) 29

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ABC037-D • I couldn't pass with Ruby ! • Traversing 1000x1000 maze • Maybe with Ruby3...? RubyKaigi 2016 Kyoto LT (2016-09-10) 31

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Crystal passes ※CrystalɿRuby-like sta0cally typed language RubyKaigi 2016 Kyoto LT (2016-09-10) 32

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Pypy2 passes ※Pypy2ɿFaster Python implemanta2on RubyKaigi 2016 Kyoto LT (2016-09-10) 33

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Python3 passes!? ! RubyKaigi 2016 Kyoto LT (2016-09-10) 34

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(DON'T TRY THIS AT HOME !) RubyKaigi 2016 Kyoto LT (2016-09-10) 38