Swiftプログラマのための今さら聞けない計算量の話

もっさりアプリをサクサクにするための基本の「キ」

Transcript

1. SwiftϓϩάϥϚͷͨΊͷ ࠓ͞Βฉ͚ͳ͍ܭࢉྔͷ࿩ ΋ͬ͞ΓΞϓϦΛαΫαΫʹ͢ΔͨΊͷجຊͷʮΩʯ SwiftϓϩάϥϚͷͨΊͷࠓ͞Βฉ͚ͳ͍ܭࢉྔͷ࿩ / iOSDC Japan 2017 / © Hisakuni Fujimoto, 2017 1
2. ࣗݾ঺հ • ౻ຊঘ๜ (53ࡀɺ1964ੜ) • ϑϦʔϥϯεϓϩάϥϚ • fhisa (Twitter, GitHub ͳͲ) • RubyCocoa(2001-), SwiftyLayout(2015-) • Cocoaษڧձ (Bukuro.swiftɺؔ౦swiftษڧձ) SwiftϓϩάϥϚͷͨΊͷࠓ͞Βฉ͚ͳ͍ܭࢉྔͷ࿩ / iOSDC Japan 2017 / © Hisakuni Fujimoto, 2017 2
3. ΞδΣϯμ • ܭࢉྔ௒ೖ໳ • Swift Standard Library ͱܭࢉྔ • ·ͱΊ SwiftϓϩάϥϚͷͨΊͷࠓ͞Βฉ͚ͳ͍ܭࢉྔͷ࿩ / iOSDC Japan 2017 / © Hisakuni Fujimoto, 2017 3
4. ܭࢉྔ௒ೖ໳ SwiftϓϩάϥϚͷͨΊͷࠓ͞Βฉ͚ͳ͍ܭࢉྔͷ࿩ / iOSDC Japan 2017 / © Hisakuni Fujimoto, 2017 4
5. ܭࢉྔ௒ೖ໳ Complexity: O(1) if the collection conforms to RandomAccessCollection; otherwise, O(n), where n is the length of the collection. — countϓϩύςΟͷυΩϡϝϯτΑΓൈਮ SwiftϓϩάϥϚͷͨΊͷࠓ͞Βฉ͚ͳ͍ܭࢉྔͷ࿩ / iOSDC Japan 2017 / © Hisakuni Fujimoto, 2017 5
6. ܭࢉྔ௒ೖ໳ Complexity: O(1) if the collection conforms to RandomAccessCollection; otherwise, O(n), where n is the length of the collection. O(1) ΍ O(n) ͸ʮܭࢉྔʯ ΞϧΰϦζϜͷෳࡶ͞Λද͢ࢦඪ SwiftϓϩάϥϚͷͨΊͷࠓ͞Βฉ͚ͳ͍ܭࢉྔͷ࿩ / iOSDC Japan 2017 / © Hisakuni Fujimoto, 2017 6
7. ΞϧΰϦζϜͱ͸ʁ ໰୊Λղͨ͘Ίͷखॱ SwiftϓϩάϥϚͷͨΊͷࠓ͞Βฉ͚ͳ͍ܭࢉྔͷ࿩ / iOSDC Japan 2017 / © Hisakuni Fujimoto, 2017 7
8. ΞϧΰϦζϜͱ͸ʁ • ୔ࢁͷσʔλ͔ΒಛఆσʔλΛݟ͚ͭΔํ๏ (ೋ෼୳ࡧͳͲ) • ୔ࢁͷσʔλΛॱʹฒ΂Δํ๏ (ϚʔδιʔτͳͲ) • ࠷େެ໿਺ΛٻΊΔํ๏ (ϢʔΫϦουͷޓআ๏) • ύζϧΛղ͘ํ๏ (ϋϊΠͷౝͳͲ) SwiftϓϩάϥϚͷͨΊͷࠓ͞Βฉ͚ͳ͍ܭࢉྔͷ࿩ / iOSDC Japan 2017 / © Hisakuni Fujimoto, 2017 8
9. ܭࢉྔ(Complexity)ͱ͸ʁ ͋ΔΞϧΰϦζϜΛ࣮ߦ͢Δͱ͖ɺೖྗͷେ͖͞ʹରͯ͠ɺͲͷ ͘Β͍ͷ࣌ؒ·ͨ͸(ϝϞϦʔ)ۭ͕ؒඞཁ͔Λද͢ࢦඪɾ໨҆ SwiftϓϩάϥϚͷͨΊͷࠓ͞Βฉ͚ͳ͍ܭࢉྔͷ࿩ / iOSDC Japan 2017 / © Hisakuni Fujimoto, 2017 9
10. ܭࢉྔ͸໨҆ • ͬ͘͟Γͱݟੵ΋Δ͜ͱ͕ॏཁ • ਖ਼֬ʹ஋Λܭࢉ͢Δ΋ͷͰ͸ͳ͍ SwiftϓϩάϥϚͷͨΊͷࠓ͞Βฉ͚ͳ͍ܭࢉྔͷ࿩ / iOSDC Japan 2017 / © Hisakuni Fujimoto, 2017 10
11. ࣌ؒܭࢉྔͱۭؒܭࢉྔ • ࣌ؒܭࢉྔ (Time complexity) ʹ ඞཁͳ࣌ؒͷ໨҆ • ۭؒܭࢉྔ (Space complexity) ʹ ඞཁͳϝϞϦʔۭؒͷ໨҆ ࣮ࡍʹ͸୯ʹʮܭࢉྔʯͱදݱ͞ΕΔ͜ͱ͕ଟ͍ɻ ͦͷ৔߹ʮ࣌ؒܭࢉྔʯͷ͜ͱΛࢦ͢ɻ SwiftϓϩάϥϚͷͨΊͷࠓ͞Βฉ͚ͳ͍ܭࢉྔͷ࿩ / iOSDC Japan 2017 / © Hisakuni Fujimoto, 2017 11
12. O(1) ܭࢉྔ ʹ ೖྗͷେ͖͞ʹؔ܎ͳ͘Ұఆ (ྫ) ഑ྻͷ n ൪໨ͷཁૉ΁ͷΞΫηε SwiftϓϩάϥϚͷͨΊͷࠓ͞Βฉ͚ͳ͍ܭࢉྔͷ࿩ / iOSDC Japan 2017 / © Hisakuni Fujimoto, 2017 12
13. O(n) ܭࢉྔ ʹ ೖྗͷେ͖͞ʹൺྫ (ྫ) ഑ྻͷ࠷ॳ͔Β n ൪໨·Ͱͷશͯͷσʔλʹॱ൪ʹΞΫηε SwiftϓϩάϥϚͷͨΊͷࠓ͞Βฉ͚ͳ͍ܭࢉྔͷ࿩ / iOSDC Japan 2017 / © Hisakuni Fujimoto, 2017 13
14. Α͋͘Δܭࢉྔ ܭࢉྔ (Oه๏) SwiftυΩϡϝϯτ O(1) ◦ O(n) ◦ O(log n) × ೋ෼୳ࡧͳͲ O(n log n) × ϚʔδιʔτͳͲͷฒ ΂ସ͑ΞϧΰϦζϜ SwiftϓϩάϥϚͷͨΊͷࠓ͞Βฉ͚ͳ͍ܭࢉྔͷ࿩ / iOSDC Japan 2017 / © Hisakuni Fujimoto, 2017 14
15. SwiftϓϩάϥϚͷͨΊͷࠓ͞Βฉ͚ͳ͍ܭࢉྔͷ࿩ / iOSDC Japan 2017 / © Hisakuni Fujimoto, 2017 15
16. Swift Standard Library ͱܭࢉྔ https://developer.apple.com/documentation/swift SwiftϓϩάϥϚͷͨΊͷࠓ͞Βฉ͚ͳ͍ܭࢉྔͷ࿩ / iOSDC Japan 2017 / © Hisakuni Fujimoto, 2017 16
17. Swift Standard Library ͱܭࢉྔ ίϨΫγϣϯʹؔ͢ΔυΩϡϝϯτͷཁॴཁॴͰɺ ܭࢉྔʹ͍ͭͯͷهड़͕͋Δɻ ഑ྻ(Array)ɺࣙॻ(Dictionary)ɺू߹(Set)ͳͲ SwiftϓϩάϥϚͷͨΊͷࠓ͞Βฉ͚ͳ͍ܭࢉྔͷ࿩ / iOSDC Japan 2017 / © Hisakuni Fujimoto, 2017 17
18. Swift Standard Library ͱܭࢉྔ υΩϡϝϯτʹग़ݱ͢Δ༻ޠ O(1), O(n) O(m), O(n + m) 2ͭͷίϨΫγϣϯ͕བྷΉܭࢉ Complexity ܭࢉྔ Amortized (complexity) ۉ͠(ܭࢉྔ) SwiftϓϩάϥϚͷͨΊͷࠓ͞Βฉ͚ͳ͍ܭࢉྔͷ࿩ / iOSDC Japan 2017 / © Hisakuni Fujimoto, 2017 18
19. Sequence ϓϩτίϧ • ͦΕͧΕͷཁૉʹ܁Γฦ͠ΞΫηεͰ͖ΔܕΛఏڙ • for i in γʔέϯε { ... } • filter, map, reduce ͳͲͷϝιουΛ࣮૷ SwiftϓϩάϥϚͷͨΊͷࠓ͞Βฉ͚ͳ͍ܭࢉྔͷ࿩ / iOSDC Japan 2017 / © Hisakuni Fujimoto, 2017 19
20. Sequence ϓϩτίϧ Expected Performance: A sequence should provide its iterator in O(1). The Sequence protocol makes no other requirements about element access, so routines that traverse a sequence should be considered O(n) unless documented otherwise.1 • γʔέϯε͸ɺཁૉͷ܁Γฦ͠Λ O(1) Ͱఏڙ͢΂͖ • ཁૉΛॱʹͨͲΔॲཧͷܭࢉྔ͸ O(n) 1 https://developer.apple.com/documentation/swift/sequence SwiftϓϩάϥϚͷͨΊͷࠓ͞Βฉ͚ͳ͍ܭࢉྔͷ࿩ / iOSDC Japan 2017 / © Hisakuni Fujimoto, 2017 20
21. countϓϩύςΟ Complexity: O(1) if the collection conforms to RandomAccessCollection; otherwise, O(n), where n is the length of the collection.2 ʮίϨΫγϣϯ͕ RandomAccessCollection ϓϩτίϧʹ४ڌ͠ ͍ͯΔ৔߹͸ O(1)ɺͦͷଞͷ৔߹͸ O(n)ʯ 2 https://developer.apple.com/documentation/swift/collection/2885508-count SwiftϓϩάϥϚͷͨΊͷࠓ͞Βฉ͚ͳ͍ܭࢉྔͷ࿩ / iOSDC Japan 2017 / © Hisakuni Fujimoto, 2017 21
22. countϓϩύςΟ Discussion: To check whether a collection is empty, use its isEmpty property instead of comparing count to zero. Unless the collection guarantees random-access performance, calculating count can be an O(n) operation.2 ʮίϨΫγϣϯ͕ۭ͔Ͳ͏͔ௐ΂ΔͨΊʹ͸ɺcount Λθϩͱൺ ֱ͢ΔͷͰ͸ͳ͘ɺisEmpty ϓϩύςΟΛ࢖͍ͳ͍͞ʯ 2 https://developer.apple.com/documentation/swift/collection/2885508-count SwiftϓϩάϥϚͷͨΊͷࠓ͞Βฉ͚ͳ͍ܭࢉྔͷ࿩ / iOSDC Japan 2017 / © Hisakuni Fujimoto, 2017 22
23. isEmptyϓϩύςΟ Complexity: O(1)3 3 https://developer.apple.com/documentation/swift/collection/2886121-isempty SwiftϓϩάϥϚͷͨΊͷࠓ͞Βฉ͚ͳ͍ܭࢉྔͷ࿩ / iOSDC Japan 2017 / © Hisakuni Fujimoto, 2017 23
24. isEmptyϓϩύςΟ Discussion: When you need to check whether your collection is empty, use the isEmpty property instead of checking that the count property is equal to zero. ... 3 ʮίϨΫγϣϯ͕ۭ͔Ͳ͏͔ௐ΂ΔͨΊʹ͸ɺcount Λθϩͱൺ ֱ͢ΔͷͰ͸ͳ͘ɺisEmpty ϓϩύςΟΛ࢖͍ͳ͍͞ʯ 3 https://developer.apple.com/documentation/swift/collection/2886121-isempty SwiftϓϩάϥϚͷͨΊͷࠓ͞Βฉ͚ͳ͍ܭࢉྔͷ࿩ / iOSDC Japan 2017 / © Hisakuni Fujimoto, 2017 24
25. ۉ͠ܭࢉྔ (Amortized complexity) ۉ͠ܭࢉྔ = ܭࢉྔͷฏۉ ࠷ѱͷܭࢉྔ͚ͩΛݟΔͷ͕൵؍తʹա͗Δͱ͖ʹɺ ܭࢉྔͷฏۉΛݟΔ4 4 ʮಈత഑ྻ΁ͷ௥Ճίετ͸ͳͥ O(1)?ʯ: http://chasen.org/~taku/blog/archives/2007/02/_o1.html SwiftϓϩάϥϚͷͨΊͷࠓ͞Βฉ͚ͳ͍ܭࢉྔͷ࿩ / iOSDC Japan 2017 / © Hisakuni Fujimoto, 2017 25
26. appendϝιου Complexity: Amortized O(1) over many additions. ... 5 Swift ͷArrayܕͷΑ͏ʹ ༰ྔΛഒʑ(ࢦ਺త)ʹ૿΍͍ͯ͘͠ಈత഑ྻͷ ʮۉ͠ܭࢉྔʯ͸ O(1) 4 6 6 reserveCapacity: https://developer.apple.com/documentation/swift/array/1538966-reservecapacity 4 ʮಈత഑ྻ΁ͷ௥Ճίετ͸ͳͥ O(1)?ʯ: http://chasen.org/~taku/blog/archives/2007/02/_o1.html 5 https://developer.apple.com/documentation/swift/array/1538872-append SwiftϓϩάϥϚͷͨΊͷࠓ͞Βฉ͚ͳ͍ܭࢉྔͷ࿩ / iOSDC Japan 2017 / © Hisakuni Fujimoto, 2017 26
27. ·ͱΊ • ܭࢉྔ ʹ ΞϧΰϦζϜͷ࣮ߦʹඞཁͳ࣌ؒɾۭؒͷ໨҆ • O(1) ʹ ೖྗʹΑΒͣɺܭࢉྔ͕Ұఆ • O(n) ʹ ೖྗʹൺྫͯ͠ɺܭࢉྔ͕૿Ճ • `Swift ͷυΩϡϝϯτͷܭࢉྔʹ͍ͭͯͷهड़ʹ໨Λ௨ͦ͏ • ܭࢉྔʹؾΛ࢖ͬͯɺ͘͘͞͞ಈ͘ΞϓϦΛ࡞Ζ͏ SwiftϓϩάϥϚͷͨΊͷࠓ͞Βฉ͚ͳ͍ܭࢉྔͷ࿩ / iOSDC Japan 2017 / © Hisakuni Fujimoto, 2017 27
28. ·ͱΊ • ܭࢉྔ ʹ ΞϧΰϦζϜͷ࣮ߦʹඞཁͳ࣌ؒɾۭؒͷ໨҆ • O(1) ʹ ೖྗʹΑΒͣɺܭࢉྔ͕Ұఆ • O(n) ʹ ೖྗʹൺྫͯ͠ɺܭࢉྔ͕૿Ճ • `Swift ͷυΩϡϝϯτͷܭࢉྔʹ͍ͭͯͷهड़ʹ໨Λ௨ͦ͏ • ܭࢉྔʹؾΛ࢖ͬͯɺ͘͘͞͞ಈ͘ΞϓϦΛ࡞Ζ͏ SwiftϓϩάϥϚͷͨΊͷࠓ͞Βฉ͚ͳ͍ܭࢉྔͷ࿩ / iOSDC Japan 2017 / © Hisakuni Fujimoto, 2017 28
29. ͝੩ௌɺ͋Γ͕ͱ͏͍͟͝·ͨ͠ʂ !! iOSDC JAPAN 2017 ָ͠Έ·͠ΐ͏ !! εϥΠυ͸ͪ͜Β https://speakerdeck.com/fhisa/ swiftpuroguramafalsetamefalsejin-sarawen-kenaiji-suan-liang- falsehua SwiftϓϩάϥϚͷͨΊͷࠓ͞Βฉ͚ͳ͍ܭࢉྔͷ࿩ / iOSDC Japan 2017 / © Hisakuni Fujimoto, 2017 29