Merge pull request kodecocodes#1 from raywenderlich/master

Refreshing since Fork

Author: billbarbour

.github/CONTRIBUTING.md

@@ -0,0 +1,59 @@
+# 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**
+
+Our repo is all about learning. The `README` file is the cake, and the sample code is the cherry on top. A good contribution has succinct explanations supported by diagrams. Code is best introduced in chunks, weaved into the explanations where relevant. 
+
+> When choosing between brievity and performance, err to the side of brievity as long as the time complexity of the particular implementation is the same. You can make a note afterwards suggesting a more performant way of doing things. 
+
+**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 +1,7 @@
+### 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 :]"

.travis.yml

@@ -1,41 +1,54 @@
 language: objective-c
-osx_image: xcode8
+osx_image: xcode9
 # sudo: false
 
 install:
 
+- gem install xcpretty-travis-formatter
 # - ./install_swiftlint.sh
 
 script:
 
-# - xcodebuild test -project ./All-Pairs\ Shortest\ Paths/APSP/APSP.xcodeproj -scheme APSPTests
-- xcodebuild test -project ./Array2D/Tests/Tests.xcodeproj -scheme Tests
-- xcodebuild test -project ./AVL\ Tree/Tests/Tests.xcodeproj -scheme Tests
-- xcodebuild test -project ./Binary\ Search/Tests/Tests.xcodeproj -scheme Tests
-# - xcodebuild test -project ./Binary\ Search\ Tree/Solution\ 1/Tests/Tests.xcodeproj -scheme Tests
-- xcodebuild test -project ./Bloom\ Filter/Tests/Tests.xcodeproj -scheme Tests
-# - xcodebuild test -project ./Bounded\ Priority\ Queue/Tests/Tests.xcodeproj -scheme Tests
-# - xcodebuild test -project ./Breadth-First\ Search/Tests/Tests.xcodeproj -scheme Tests
-# - xcodebuild test -project ./Bucket\ Sort/Tests/Tests.xcodeproj -scheme Tests
-- xcodebuild test -project ./B-Tree/Tests/Tests.xcodeproj -scheme Tests
-# - xcodebuild test -project ./Counting\ Sort/Tests/Tests.xcodeproj -scheme Tests
-# - xcodebuild test -project ./Depth-First\ Search/Tests/Tests.xcodeproj -scheme Tests
-# - xcodebuild test -project ./Graph/Graph.xcodeproj -scheme GraphTests
-# - xcodebuild test -project ./Heap/Tests/Tests.xcodeproj -scheme Tests
-# - xcodebuild test -project ./Heap\ Sort/Tests/Tests.xcodeproj -scheme Tests
-- xcodebuild test -project ./Insertion\ Sort/Tests/Tests.xcodeproj -scheme Tests
-# - xcodebuild test -project ./K-Means/Tests/Tests.xcodeproj -scheme Tests
-# - xcodebuild test -project ./Linked\ List/Tests/Tests.xcodeproj -scheme Tests
-- xcodebuild test -project ./Longest\ Common\ Subsequence/Tests/Tests.xcodeproj -scheme Tests
-# - xcodebuild test -project ./Minimum\ Spanning\ Tree\ \(Unweighted\)/Tests/Tests.xcodeproj -scheme Tests
-# - xcodebuild test -project ./Priority\ Queue/Tests/Tests.xcodeproj -scheme Tests
-- xcodebuild test -project ./Queue/Tests/Tests.xcodeproj -scheme Tests
-# - xcodebuild test -project ./Quicksort/Tests/Tests.xcodeproj -scheme Tests
-# - xcodebuild test -project ./Run-Length\ Encoding/Tests/Tests.xcodeproj -scheme Tests
-# - xcodebuild test -project ./Select\ Minimum\ Maximum/Tests/Tests.xcodeproj -scheme Tests
-- xcodebuild test -project ./Selection\ Sort/Tests/Tests.xcodeproj -scheme Tests
-# - xcodebuild test -project ./Shell\ Sort/Tests/Tests.xcodeproj -scheme Tests
-# - xcodebuild test -project ./Shortest\ Path\ \(Unweighted\)/Tests/Tests.xcodeproj -scheme Tests
-# - xcodebuild test -project ./Single-Source\ Shortest\ Paths\ \(Weighted\)/SSSP.xcodeproj -scheme SSSPTests
-- xcodebuild test -project ./Stack/Tests/Tests.xcodeproj -scheme Tests
-# - xcodebuild test -project ./Topological\ Sort/Tests/Tests.xcodeproj -scheme Tests
+- xcodebuild test -project ./Array2D/Tests/Tests.xcodeproj -scheme Tests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./All-Pairs\ Shortest\ Paths/APSP/APSP.xcodeproj -scheme APSPTests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./AVL\ Tree/Tests/Tests.xcodeproj -scheme Tests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./Binary\ Search/Tests/Tests.xcodeproj -scheme Tests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./Boyer-Moore-Horspool/Tests/Tests.xcodeproj -scheme Tests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./Binary\ Search\ Tree/Solution\ 1/Tests/Tests.xcodeproj -scheme Tests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./Bloom\ Filter/Tests/Tests.xcodeproj -scheme Tests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./Bounded\ Priority\ Queue/Tests/Tests.xcodeproj -scheme Tests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./Breadth-First\ Search/Tests/Tests.xcodeproj -scheme Tests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./Bucket\ Sort/Tests/Tests.xcodeproj -scheme Tests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./B-Tree/Tests/Tests.xcodeproj -scheme Tests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./Comb\ Sort/Tests/Tests.xcodeproj -scheme Tests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./Convex\ Hull/Convex\ Hull.xcodeproj -scheme Tests -destination 'platform=iOS Simulator,name=iPhone 7,OS=11.0' | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./Counting\ Sort/Tests/Tests.xcodeproj -scheme Tests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./Depth-First\ Search/Tests/Tests.xcodeproj -scheme Tests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./Graph/Graph.xcodeproj -scheme GraphTests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./Heap/Tests/Tests.xcodeproj -scheme Tests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./Heap\ Sort/Tests/Tests.xcodeproj -scheme Tests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./Insertion\ Sort/Tests/Tests.xcodeproj -scheme Tests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./K-Means/Tests/Tests.xcodeproj -scheme Tests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./Linked\ List/Tests/Tests.xcodeproj -scheme Tests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./Singly\ Linked\ List/Tests/Tests.xcodeproj -scheme Tests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./Longest\ Common\ Subsequence/Tests/Tests.xcodeproj -scheme Tests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./Minimum\ Spanning\ Tree\ \(Unweighted\)/Tests/Tests.xcodeproj -scheme Tests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./Priority\ Queue/Tests/Tests.xcodeproj -scheme Tests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./Queue/Tests/Tests.xcodeproj -scheme Tests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./Quicksort/Tests/Tests-Quicksort.xcodeproj -scheme Test-Quicksort | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./Radix\ Sort/Tests/Tests.xcodeproj -scheme Tests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./Rootish\ Array\ Stack/Tests/Tests.xcodeproj -scheme Tests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./Select\ Minimum\ Maximum/Tests/Tests.xcodeproj -scheme Tests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./Selection\ Sort/Tests/Tests.xcodeproj -scheme Tests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./Shell\ Sort/Tests/Tests.xcodeproj -scheme Tests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./Shortest\ Path\ \(Unweighted\)/Tests/Tests.xcodeproj -scheme Tests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./Single-Source\ Shortest\ Paths\ \(Weighted\)/SSSP.xcodeproj -scheme SSSPTests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./Stack/Tests/Tests.xcodeproj -scheme Tests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./Topological\ Sort/Tests/Tests.xcodeproj -scheme Tests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./Treap/Treap/Treap.xcodeproj -scheme Tests | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./Palindromes/Test/Test.xcodeproj -scheme Test | xcpretty -f `xcpretty-travis-formatter`
+- xcodebuild test -project ./Ternary\ Search\ Tree/Tests/Tests.xcodeproj -scheme Tests | xcpretty -f `xcpretty-travis-formatter`
+
+after_success:
+
+- if [[ "$TRAVIS_BRANCH" == "master" ]]; then ./gfm-render.sh; fi

3Sum and 4Sum/3Sum.playground/Contents.swift

@@ -0,0 +1,63 @@
+
+extension Collection where Element: Equatable {
+  
+  /// In a sorted collection, replaces the given index with a successor mapping to a unique element.
+  ///
+  /// - Parameter index: A valid index of the collection. `index` must be less than `endIndex`
+  func formUniqueIndex(after index: inout Index) {
+    var prev = index
+    repeat {
+      prev = index
+      formIndex(after: &index)
+    } while index < endIndex && self[prev] == self[index]
+  }
+}
+
+extension BidirectionalCollection where Element: Equatable {
+  
+  /// In a sorted collection, replaces the given index with a predecessor that maps to a unique element.
+  ///
+  /// - Parameter index: A valid index of the collection. `index` must be greater than `startIndex`.
+  func formUniqueIndex(before index: inout Index) {
+    var prev = index
+    repeat {
+      prev = index
+      formIndex(before: &index)
+    } while index > startIndex && self[prev] == self[index]
+  }
+}
+
+func threeSum<T: BidirectionalCollection>(_ collection: T, target: T.Element) -> [[T.Element]] where T.Element: Numeric & Comparable {
+  let sorted = collection.sorted()
+  var ret: [[T.Element]] = []
+  var l = sorted.startIndex
+  
+  ThreeSum: while l < sorted.endIndex { defer { sorted.formUniqueIndex(after: &l) }
+    var m = sorted.index(after: l)
+    var r = sorted.index(before: sorted.endIndex)
+    
+    TwoSum: while m < r && r < sorted.endIndex { 
+      let sum = sorted[l] + sorted[m] + sorted[r]
+      if sum == target {
+        ret.append([sorted[l], sorted[m], sorted[r]])
+        sorted.formUniqueIndex(after: &m)
+        sorted.formUniqueIndex(before: &r)
+      } else if sum < target {
+        sorted.formUniqueIndex(after: &m)
+      } else {
+        sorted.formUniqueIndex(before: &r)
+      }
+    }
+  }
+  
+  return ret
+}
+
+// Answer: [[-1, 0, 1], [-1, -1, 2]]
+threeSum([-1, 0, 1, 2, -1, -4], target: 0)
+
+// Answer: [[-1, -1, 2], [-1, 0, 1]]
+threeSum([-1, -1, -1, -1, 2, 1, -4, 0], target: 0)
+
+// Answer: [[-1, -1, 2]]
+threeSum([-1, -1, -1, -1, -1, -1, 2], target: 0)

Red-Black Tree/Red-Black Tree 2.playground/contents.xcplayground renamed to 3Sum and 4Sum/3Sum.playground/contents.xcplayground

@@ -0,0 +1,59 @@
+extension Collection where Element: Equatable {
+  
+  /// In a sorted collection, replaces the given index with a successor mapping to a unique element.
+  ///
+  /// - Parameter index: A valid index of the collection. `index` must be less than `endIndex`
+  func formUniqueIndex(after index: inout Index) {
+    var prev = index
+    repeat {
+      prev = index
+      formIndex(after: &index)
+    } while index < endIndex && self[prev] == self[index]
+  }
+}
+
+extension BidirectionalCollection where Element: Equatable {
+  
+  /// In a sorted collection, replaces the given index with a predecessor that maps to a unique element.
+  ///
+  /// - Parameter index: A valid index of the collection. `index` must be greater than `startIndex`.
+  func formUniqueIndex(before index: inout Index) {
+    var prev = index
+    repeat {
+      prev = index
+      formIndex(before: &index)
+    } while index > startIndex && self[prev] == self[index]
+  }
+}
+
+func fourSum<T: BidirectionalCollection>(_ collection: T, target: T.Element) -> [[T.Element]] where T.Element: Numeric & Comparable {
+  let sorted = collection.sorted()
+  var ret: [[T.Element]] = []
+  
+  var l = sorted.startIndex
+  FourSum: while l < sorted.endIndex { defer { sorted.formUniqueIndex(after: &l) }
+    var ml = sorted.index(after: l)
+                                      
+    ThreeSum: while ml < sorted.endIndex { defer { sorted.formUniqueIndex(after: &ml) }
+      var mr = sorted.index(after: ml)
+      var r = sorted.index(before: sorted.endIndex)
+      
+      TwoSum: while mr < r && r < sorted.endIndex {
+        let sum = sorted[l] + sorted[ml] + sorted[mr] + sorted[r]
+        if sum == target {
+          ret.append([sorted[l], sorted[ml], sorted[mr], sorted[r]])
+          sorted.formUniqueIndex(after: &mr)
+          sorted.formUniqueIndex(before: &r)
+        } else if sum < target {
+          sorted.formUniqueIndex(after: &mr)
+        } else {
+          sorted.formUniqueIndex(before: &r)
+        }
+      }
+    }
+  }
+  return ret
+}
+
+// answer: [[-2, -1, 1, 2], [-2, 0, 0, 2], [-1, 0, 0, 1]]
+fourSum([1, 0, -1, 0, -2, 2], target: 0)