木の上を歩こう

グラフ理論における木の紹介。例として 二分木を Rust でstep by step で実装。

Transcript

1. ໦ͷ্Λา͜͏ @hama_du CombGig3 on 2018/09/09
2. ໦ͷΠςϨʔλΛ RustͰ࣮૷͠Α͏ [͓୊]
3. ໦ʁ
5. ✋͕͍ͪ·͢
6. ͜ɹΜɹͳɹͷ (άϥϑཧ࿦ͷ༻ޠͰ͢)
7. ·ͣ͸άϥϑ͍ͭͯઆ໌
8. ௖఺ͱลͰϞϊಉ࢜ͷؔ܎Λද͢ ؙ͕
   ௖఺ ઢ͕
   ล
9. ஍Լమͷ࿏ઢਤ ը૾ͷग़య: ࿏ઢɾӺͷ৘ใ | ౦ژϝτϩ / https://www.tokyometro.jp/station/
10. ஍Լమͷ࿏ઢਤ
11. ΢ΣϒϖʔδͷϦϯΫ
12. ΢ΣϒϖʔδͷϦϯΫ ※ؔ܎ͷʮ޲͖ʯʹҙຯ͕͋Δͱ͖͸্ਤͷΑ͏ʹ໼ҹʹ޲͖͕෇͍ͨʮ༗޲άϥϑʯΛ࢖͏͜ͱ͕͋Γ·͢ɻ ຊൃදʹ͓͍ͯ͸ৄ͘͠͸ཱͪೖΓ·ͤΜɻ ը૾ͷग़య: Topology of the 2012 WDC Hyperlink Graph / http://webdatacommons.org/hyperlinkgraph/2012-08/topology.html
13. ফඅऀͷߪങ৘ใ
14. ফඅऀͷߪങ৘ใ
15. ͋Ε΋͜Ε΋ ࣮͸άϥϑ
16. ໦͸ಛผͳάϥϑ
17. [໦ͷఆٛ] ด࿏(ϧʔϓ)͕ͳ͍ ࿈݁ͳάϥϑ
18. ໦ͷಛ௃
19. ࠜΛܾΊΔͱ͍Ζ͍Ζศར
20. ࠜ
    SPPU ༿
    MFBG ࢠ
    DIJME
21. ࠜҎ֎ͷ਌͕1ͭʹఆ·Δ
22. ௖఺ ͷ਌ ਌ͷ਌ ࠜͷ਌͸
    ͳ͍
23. ࢠ΋ͦΕͧΕ໦ ʢ෦෼໦ʣ
24. ɿ෦෼໦
25. ໦͸ ࠶ؼతͳʮ֊૚ߏ଄ʯʹ ࣗવʹग़ݱ͢Δ
26. σΟϨΫτϦͷ࿦ཧߏ଄
27. htmlͷߏ଄
28. JSONͷߏ଄
29. ͋Ε΋͜Ε΋ ࣮͸໦
30. ͔͜͜Β Rust (࣮૷) ύʔτͰ͢
31. ໦ͷΠςϨʔλΛ RustͰ࣮૷͠Α͏ [͓୊(࠶ܝ)]
32. ࠓճ͸ೋ෼໦Λѻ͏ ࠨͷࢠ ӈͷࢠ
33. 1. ೋ෼໦Λ࣮૷͠Α͏ 2. ΠςϨʔλΛ࣮૷͠Α͏
34. 1. ೋ෼໦Λ࣮૷͠Α͏
35. ೋ෼໦ͷදݱ struct BinaryTree { left: Option<Box<BinaryTree>>, right: Option<Box<BinaryTree>> } ώʔϓ΁ͷϙΠϯλ pub enum Option<T> { None, Some(T), }
36. ௖఺ʹ஋Λ࣋ͨͤΑ͏ struct BinaryTree { value: i32, left: Option<Box<BinaryTree>>, right: Option<Box<BinaryTree>> }
37. ίϯετϥΫλ impl BinaryTree { fn new(value: i32, left: Option<BinaryTree>, right: Option<BinaryTree>) -> Self { BinaryTree { value, left: left.map(|l| Box::new(l)), right: right.map(|r| Box::new(r)) } } }
38. ؆୯ʹ༿Λ࡞ΕΔΑ͏ʹ impl BinaryTree { fn leaf(value: i32) -> Self { BinaryTree { value, left: None, right: None } } }
39. ࢼ͠ʹग़ྗ fn main() { let tree = BinaryTree::new( 3, Some(BinaryTree::new( 7, (ུ) )), Some(BinaryTree::new( 2, (ུ) )) ); println!(“{:?}”, tree); } ͜͜·Ͱͷ಺༰ͷRust Playground: https://play.rust-lang.org/? gist=64cde6d75f21c94c785116cb86c8d97c&version=stable&mode=debug&edition=2015
40. 2. ΠςϨʔλΛ࣮૷͠Α͏
41. Iterator τϨΠτ trait Iterator { type Item; fn next(&mut self) -> Option<Self::Item>; }
42. ϕΫλ(഑ྻ)ͷΠςϨʔλ
43. ໦ͷΠςϨʔλ
44. ḷΔॱ൪ΛܾΊΑ͏
45. ࣗ਎ˠࠨͷࢠˠӈͷࢠͷॱ൪Ͱ
46. Iterator Λ࣮૷͢Δ…ʁ impl Iterator for BinaryTree { type Item = i32; fn next(&mut self) -> Option<i32> { // Ͳ͏͠Α͏ɾɾɾʁ } }
47. Iterator Λ࣮૷͢Δʹ͸ ঢ়ଶ͕ඞཁ
48. ࣍ʹݟΔ΂͖௖఺͸Ͳ͔͜ Ұཡʹͯ͠อ࣋͢Δ
49. BinaryTreeIterator struct BinaryTreeIterator { cur: Vec<BinaryTree> } impl Iterator for BinaryTreeIterator { type Item = i32; fn next(&mut self) -> Option<i32> { // ͜͜Λ࣮૷͢Δ } }
50. BinaryTreeIterator - next fn next(&mut self) -> Option<i32> { if self.cur.len() == 0 { None } else { let node = self.cur.pop().unwrap(); if let Some(right) = node.right { self.cur.push(*right); } if let Some(left) = node.left { self.cur.push(*left); } Some(node.value) } }
51. BinaryTreeIteratorΛ࡞Δ impl BinaryTree { fn into_iter(self) -> BinaryTreeIterator { BinaryTreeIterator { cur: vec![self] } } }
52. ࢼ͠ʹา͜͏ fn main() { let tree = … let mut iter = tree.into_iter(); println!(“{:?}”, iter.next()); // Some(3) println!(“{:?}”, iter.next()); // Some(7) println!(“{:?}”, iter.next()); // Some(1) println!(“{:?}”, iter.next()); // Some(5) // … }
53. ͜͜·ͰͰ͖Ε͹ ศརͳಓ۩͕ͨͪ࢖͑Δ
54. forจͱ࢖͏ fn main() { let tree = … for value in tree.into_iter() { println!("{}", value); } } ͜͜·Ͱͷ಺༰ͷRust Playground: https://play.rust-lang.org/? gist=f0ddf0692e9cf0217899c0354305cc5d&version=stable&mode=debug&edition=2015
55. step_by fn main() { let tree = … for value in tree.into_iter().step_by(2) { println!("{}", value); } }
56. map fn main() { let tree = … let dbl: Vec<i32> = tree .into_iter() .map(|x| x*2).collect(); println!(“{:?}”, dbl); }
57. ໦ͷ্Λา͚·ͨ͠ʂ
58. ଞͷάϥϑσʔλߏ଄΋ ࣮૷ͯ͠༡ΜͰΈΑ͏
59. ͓ΘΓ
60. ͕࣌ؒ༨ͬͨΒ
61. ೋ෼໦ͷදݱ(NG) struct BinaryTree { left: Option<BinaryTree>, right: Option<BinaryTree> }
62. ίϯύΠϧ͢ΔͱΤϥʔ $ rustc main.rs error[E0072]: recursive type `BinaryTree` has infinite size --> src/main.rs:1:1 | 1 | struct BinaryTree { | ^^^^^^^^^^^^^^^^^ recursive type has infinite size 2 | left: Option<BinaryTree>, | ------------------------ recursive without indirection 3 | right: Option<BinaryTree> | ------------------------- recursive without indirection | = help: insert indirection (e.g., a `Box`, `Rc`, or `&`) at some point to make `BinaryTree` representable
63. why?
64. ΤϥʔϝοηʔδΛΑ͘ಡ΋͏ $ rustc main.rs error[E0072]: recursive type `BinaryTree` has infinite size --> src/main.rs:1:1 | 1 | struct BinaryTree { | ^^^^^^^^^^^^^^^^^ recursive type has infinite size 2 | left: Option<BinaryTree>, | ------------------------ recursive without indirection 3 | right: Option<BinaryTree> | ------------------------- recursive without indirection | = help: insert indirection (e.g., a `Box`, `Rc`, or `&`) at some point to make `BinaryTree` representable
65. `BinaryTree` has infinite size
66. ແݶͷαΠζ
67. ΤϥʔϝοηʔδΛΑ͘ಡ΋͏ $ rustc main.rs error[E0072]: recursive type `BinaryTree` has infinite size --> src/main.rs:1:1 | 1 | struct BinaryTree { | ^^^^^^^^^^^^^^^^^ recursive type has infinite size 2 | left: Option<BinaryTree>, | ------------------------ recursive without indirection 3 | right: Option<BinaryTree> | ------------------------- recursive without indirection | = help: insert indirection (e.g., a `Box`, `Rc`, or `&`) at some point to make `BinaryTree` representable
68. insert indirection (e.g., `Box`, `Rc`, `&`)
69. ೋ෼໦ͷදݱ(BoxΛ࢖͏) struct BinaryTree { left: Option<Box<BinaryTree>>, right: Option<Box<BinaryTree>> } ώʔϓ΁ͷϙΠϯλ
70. ϙΠϯλΛ࢖ͬͯݻఆαΠζʹ