Merge remote-tracking branch 'raywenderlich/master' into dijkstra

Author: Taras Nikulin

.github/CONTRIBUTING.md

@@ -0,0 +1,57 @@
+# Contributing Guidelines
+
+Want to help out with the Swift Algorithm Club? Great! While we don't have strict templates on the format of each contribution, we do have a few guidelines that should be kept in mind:
+
+**Readability**
+
+The `README` file is the cake, and the sample code is the cherry on top. Readablity is really important for us. A good contribution has succinct explanations supported by diagrams. Code is best introduced in chunks, weaved into the explanations where relevant. 
+
+**API Design Guidelines**
+
+A good contribution abides to the [Swift API Guidelines](https://swift.org/documentation/api-design-guidelines/). We review the pull requests with this in mind.
+
+**Swift Language Guidelines**
+
+We follow the following Swift [style guide](https://github.com/raywenderlich/swift-style-guide). 
+
+## Contribution Categories
+
+### Refinement
+
+Unit tests. Fixes for typos. No contribution is too small. :-)
+
+The repository has over 100 different data structures and algorithms. We're always interested in improvements to existing implementations and better explanations. Suggestions for making the code more Swift-like or to make it fit better with the standard library is most welcomed. 
+
+### New Contributions
+
+Before writing about something new, you should do 2 things:
+
+1. Check the main page for existing implementations
+2. Check the [pull requests](https://github.com/raywenderlich/swift-algorithm-club/pulls) for "claimed" topics. More info on that below. 
+
+If what you have in mind is a new addition, please follow this process when submitting your contribution:
+
+1. Create a pull request to "claim" an algorithm or data structure. This is to avoid having multiple people working on the same thing.
+2. Use this [style guide](https://github.com/raywenderlich/swift-style-guide) for writing code (more or less).
+3. Write an explanation of how the algorithm works. Include **plenty of examples** for readers to follow along. Pictures are good. Take a look at [the explanation of quicksort](../Quicksort/) to get an idea.
+4. Include your name in the explanation, something like *Written by Your Name* at the end of the document. 
+5. Add a playground and/or unit tests.
+
+For the unit tests:
+
+- Add the unit test project to `.travis.yml` so they will be run on [Travis-CI](https://travis-ci.org/raywenderlich/swift-algorithm-club). Add a line to `.travis.yml` like this:
+
+```
+- xctool test -project ./Algorithm/Tests/Tests.xcodeproj -scheme Tests
+```
+
+- Configure the Test project's scheme to run on Travis-CI:
+    - Open **Product -> Scheme -> Manage Schemes...**
+    - Uncheck **Autocreate schemes**
+    - Check **Shared**
+
+![Screenshot of scheme settings](../Images/scheme-settings-for-travis.png)
+
+## Want to chat?
+
+This isn't just a repo with a bunch of code... If you want to learn more about how an algorithm works or want to discuss better ways of solving problems, then open a [Github issue](https://github.com/raywenderlich/swift-algorithm-club/issues) and we'll talk!

.github/ISSUE_TEMPLATE.md

@@ -0,0 +1,13 @@
+### Category
+
+- [ ] Bug
+- [ ] Feature Request
+- [ ] Question
+
+### Brief Intro
+
+<!-- Describe the issue briefly.-->
+
+### More Details
+
+<!-- If necessary, start off with the code snippet. Put the code in between ``` to format them into code blocks.-->

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,11 @@
+<!-- Thanks for contributing to the SAC! Before you submit your pull request, please make sure to check the following boxes by putting an x in the [ ] -->
+
+### Checklist
+
+- [ ] I've looked at the [contribution guidelines](https://github.com/raywenderlich/swift-algorithm-club/blob/master/.github/CONTRIBUTING.md).
+- [ ] This pull request is complete and ready for review.
+
+### Description
+
+<!-- In a short paragraph, describe the PR --> 
+

.swiftlint.yml

@@ -17,8 +17,8 @@ disabled_rules:
 custom_rules:
   smiley_face:
     name: "Smiley Face"
-    regex: "(\:\))"
-    match_kinds: 
+    regex: '( :\))'
+    match_kinds:
       - comment
       - string
     message: "A closing parenthesis smiley :) creates a half-hearted smile, and thus is not preferred. Use :]"

AVL Tree/AVLTree.playground/Sources/AVLTree.swift

@@ -99,17 +99,11 @@ open class AVLTree<Key: Comparable, Payload> {
 
 extension TreeNode {
   public func minimum() -> TreeNode? {
-    if let leftChild = self.leftChild {
-      return leftChild.minimum()
-    }
-    return self
+    return leftChild?.minimum() ?? self
   }
 
   public func maximum() -> TreeNode? {
-    if let rightChild = self.rightChild {
-      return rightChild.maximum()
-    }
-    return self
+    return rightChild?.maximum() ?? self
   }
 }
 
@@ -120,11 +114,7 @@ extension AVLTree {
   }
 
   public func search(input: Key) -> Payload? {
-    if let result = search(key: input, node: root) {
-      return result.payload
-    } else {
-      return nil
-    }
+    return search(key: input, node: root)?.payload
   }
 
   fileprivate func search(key: Key, node: Node?) -> Node? {
@@ -385,11 +375,7 @@ extension TreeNode: CustomDebugStringConvertible {
 
 extension AVLTree: CustomDebugStringConvertible {
   public var debugDescription: String {
-    if let root = root {
-      return root.debugDescription
-    } else {
-      return "[]"
-    }
+    return root?.debugDescription ?? "[]"
   }
 }
 
@@ -409,10 +395,6 @@ extension TreeNode: CustomStringConvertible {
 
 extension AVLTree: CustomStringConvertible {
   public var description: String {
-    if let root = root {
-      return root.description
-    } else {
-      return "[]"
-    }
+    return root?.description ?? "[]"
   }
 }

AVL Tree/AVLTree.swift

@@ -99,17 +99,11 @@ open class AVLTree<Key: Comparable, Payload> {
 
 extension TreeNode {
   public func minimum() -> TreeNode? {
-    if let leftChild = self.leftChild {
-      return leftChild.minimum()
-    }
-    return self
+    return leftChild?.minimum() ?? self
   }
 
   public func maximum() -> TreeNode? {
-    if let rightChild = self.rightChild {
-      return rightChild.maximum()
-    }
-    return self
+    return rightChild?.maximum() ?? self
   }
 }
 
@@ -120,11 +114,7 @@ extension AVLTree {
   }
 
   public func search(input: Key) -> Payload? {
-    if let result = search(key: input, node: root) {
-      return result.payload
-    } else {
-      return nil
-    }
+    return search(key: input, node: root)?.payload
   }
 
   fileprivate func search(key: Key, node: Node?) -> Node? {
@@ -385,11 +375,7 @@ extension TreeNode: CustomDebugStringConvertible {
 
 extension AVLTree: CustomDebugStringConvertible {
   public var debugDescription: String {
-    if let root = root {
-      return root.debugDescription
-    } else {
-      return "[]"
-    }
+    return root?.debugDescription ?? "[]"
   }
 }
 
@@ -409,10 +395,6 @@ extension TreeNode: CustomStringConvertible {
 
 extension AVLTree: CustomStringConvertible {
   public var description: String {
-    if let root = root {
-      return root.description
-    } else {
-      return "[]"
-    }
+    return root?.description ?? "[]"
   }
 }

All-Pairs Shortest Paths/APSP/APSP/FloydWarshall.swift

@@ -175,7 +175,7 @@ public struct FloydWarshallResult<T>: APSPResult where T: Hashable {
   public func path(fromVertex from: Vertex<T>, toVertex to: Vertex<T>, inGraph graph: AbstractGraph<T>) -> [T]? {
 
     if let path = recursePathFrom(fromVertex: from, toVertex: to, path: [ to ], inGraph: graph) {
-      let pathValues = path.map() { vertex in
+      let pathValues = path.map { vertex in
         vertex.data
       }
       return pathValues

Array2D/Array2D.playground/Contents.swift

@@ -7,13 +7,13 @@ public struct Array2D<T> {
   public let columns: Int
   public let rows: Int
   fileprivate var array: [T]
-  
+
   public init(columns: Int, rows: Int, initialValue: T) {
     self.columns = columns
     self.rows = rows
     array = .init(repeating: initialValue, count: rows*columns)
   }
-  
+
   public subscript(column: Int, row: Int) -> T {
     get {
       precondition(column < columns, "Column \(column) Index is out of range. Array<T>(columns: \(columns), rows:\(rows))")

Array2D/Array2D.swift

@@ -7,13 +7,13 @@ public struct Array2D<T> {
   public let columns: Int
   public let rows: Int
   fileprivate var array: [T]
-  
+
   public init(columns: Int, rows: Int, initialValue: T) {
     self.columns = columns
     self.rows = rows
     array = .init(repeating: initialValue, count: rows*columns)
   }
-  
+
   public subscript(column: Int, row: Int) -> T {
     get {
       precondition(column < columns, "Column \(column) Index is out of range. Array<T>(columns: \(columns), rows:\(rows))")

B-Tree/BTree.playground/Contents.swift

@@ -14,8 +14,7 @@ bTree[3]
 
 bTree.remove(2)
 
-bTree.traverseKeysInOrder {
-  key in
+bTree.traverseKeysInOrder { key in
   print(key)
 }