Feedback on chapters 4-8

Classic Computer Science Problems in Swift.playground/Pages/Chapter 4.xcplaygroundpage/Contents.swift

@@ -52,7 +52,7 @@ extension Graph {
  if let i = vertices.index(of: vertex) {
  return i
  }
- return nil;
+ return nil 
  }
 
  /// Find all of the neighbors of a vertex at a given index.
@@ -90,12 +90,11 @@ extension Graph {
  }
  return nil
  }
-
  /// Add a vertex to the graph.
  ///
  /// - parameter v: The vertex to be added.
  /// - returns: The index where the vertex was added.
- public func addVertex(_ v: VertexType) -> Int {
+ @discardableResult public func addVertex(_ v: VertexType) -> Int {
  vertices.append(v)
  edges.append([EdgeType]())
  return vertices.count - 1
@@ -133,24 +132,21 @@ open class UnweightedEdge: Edge {
 open class UnweightedGraph<V: Equatable>: Graph {
  var vertices: [V] = [V]()
  var edges: [[UnweightedEdge]] = [[UnweightedEdge]]() //adjacency lists
-
- public init() {
- }
-
+
  public init(vertices: [V]) {
  for vertex in vertices {
- _ = self.addVertex(vertex)
+ self.addVertex(vertex)
  }
  }
- 
+
  /// This is a convenience method that adds an unweighted edge.
  ///
  /// - parameter from: The starting vertex's index.
  /// - parameter to: The ending vertex's index.
  public func addEdge(from: Int, to: Int) {
  addEdge(UnweightedEdge(u: from, v: to))
  }
- 
+
  /// This is a convenience method that adds an unweighted, undirected edge between the first occurence of two vertices.
  ///
  /// - parameter from: The starting vertex.
@@ -162,7 +158,7 @@ open class UnweightedGraph<V: Equatable>: Graph {
  }
  }
  }
- 
+
  /// MARK: Implement CustomStringConvertible
  public var description: String {
  var d: String = ""
@@ -324,26 +320,22 @@ open class WeightedEdge<W: Comparable & Summable>: Edge, Comparable {
 open class WeightedGraph<V: Equatable & Hashable, W: Comparable & Summable>: Graph {
  var vertices: [V] = [V]()
  var edges: [[WeightedEdge<W>]] = [[WeightedEdge<W>]]() //adjacency lists
-
- public init() {
- }
-
+
  public init(vertices: [V]) {
  for vertex in vertices {
- _ = self.addVertex(vertex)
+ self.addVertex(vertex)
  }
  }
-
  /// Find all of the neighbors of a vertex at a given index.
  ///
  /// - parameter index: The index for the vertex to find the neighbors of.
  /// - returns: An array of tuples including the vertices as the first element and the weights as the second element.
  public func neighborsForIndexWithWeights(_ index: Int) -> [(V, W)] {
- var distanceTuples: [(V, W)] = [(V, W)]();
+ var distanceTuples: [(V, W)] = [(V, W)]()
  for edge in edges[index] {
  distanceTuples += [(vertices[edge.v], edge.weight)]
  }
- return distanceTuples;
+ return distanceTuples
  }
 
  /// This is a convenience method that adds a weighted edge.
@@ -520,7 +512,7 @@ public extension WeightedGraph {
 
  return (distances, pathDict)
  }
- 
+
 
  /// A convenience version of dijkstra() that allows the supply of the root
  /// vertex instead of the index of the root vertex.
@@ -530,7 +522,7 @@ public extension WeightedGraph {
  }
  return ([], [:])
  }
- 
+
  /// Helper function to get easier access to Dijkstra results.
  public func distanceArrayToVertexDict(distances: [W?]) -> [V : W?] {
  var distanceDict: [V: W?] = [V: W?]()

Classic Computer Science Problems in Swift.playground/Pages/Chapter 5.xcplaygroundpage/Contents.swift

@@ -27,7 +27,7 @@ extension Array {
  if count < 2 { return shuffledArray } // already shuffled
  for i in (1..<count).reversed() { // count backwards
  let position = Int(arc4random_uniform(UInt32(i + 1))) // random to swap
- if i != position { // swap with the end, don't bother with selp swaps
+ if i != position { // swap with the end, don't bother with swap
  shuffledArray.swapAt(i, position)
  }
  }
@@ -210,7 +210,6 @@ final class SimpleEquation: Chromosome {
 
 let se = GeneticAlgorithm<SimpleEquation>(size: 10, threshold: 13.0, maxGenerations: 100, mutationChance: 0.1, crossoverChance: 0.7)
 let result1 = se.run()
-result1.fitness
 result1.prettyPrint()
 
 

Classic Computer Science Problems in Swift.playground/Pages/Chapter 8.xcplaygroundpage/Contents.swift

@@ -30,12 +30,14 @@ struct Item {
 func knapsack(items: [Item], maxCapacity: Int) -> [Item] {
  //build up dynamic programming table
  var table: [[Float]] = [[Float]](repeating: [Float](repeating: 0.0, count: maxCapacity + 1), count: items.count + 1) //initialize table - overshooting in size
- for i in 1...items.count {
+ for (i, item) in items.enumerated() {
  for capacity in 1...maxCapacity {
- if capacity - items[i - 1].weight >= 0 { // still room in knapsack
- table[i][capacity] = max(table[i - 1][capacity - items[i - 1].weight] + items[i - 1].value, table[i - 1][capacity]) // only take if more valuable than previous combo
+ let previousItemsValue = table[i][capacity]
+ if capacity >= item.weight { // item fits in knapsack
+ let valueFreeingWeightForItem = table[i][capacity - item.weight]
+ table[i + 1][capacity] = max(valueFreeingWeightForItem + item.value, previousItemsValue) // only take if more valuable than previous combo
  } else { // no room for this item
- table[i][capacity] = table[i - 1][capacity] //use prior combo
+ table[i + 1][capacity] = previousItemsValue //use prior combo
  }
  }
  }