BFS Added test project with implementation files.

Author: Chris Pilcher

Breadth-First Search/BreadthFirstSearch.swift

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+func breadthFirstSearch(graph: Graph, source: Node) {
+  var queue = Queue<Node>()
+  queue.enqueue(source)
+
+  print(source.label)
+
+  while !queue.isEmpty {
+    let current = queue.dequeue()!
+    for edge in current.neighbors {
+      let neighborNode = edge.neighbor
+      if !neighborNode.visited {
+        queue.enqueue(neighborNode)
+        neighborNode.visited = true
+        print(neighborNode.label)
+      }
+    }
+  }
+}

Breadth-First Search/BreadthFirstSearchMinimumSpanningTree.swift

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+func breadthFirstSearchMinimumSpanningTree(graph: Graph, source: Node) -> Graph {
+  let minimumSpanningTree = graph.duplicate()
+
+  var queue = Queue<Node>()
+  let sourceInMinimumSpanningTree = minimumSpanningTree.findNodeWithLabel(source.label)
+  queue.enqueue(sourceInMinimumSpanningTree)
+  sourceInMinimumSpanningTree.visited = true
+
+  while !queue.isEmpty {
+    let current = queue.dequeue()!
+    for edge in current.neighbors {
+      let neighborNode = edge.neighbor
+      if !neighborNode.visited {
+        neighborNode.visited = true
+        queue.enqueue(neighborNode)
+      } else {
+        current.remove(edge)
+      }
+    }
+  }
+
+  return minimumSpanningTree
+}

Breadth-First Search/BreadthFirstSearchShortestPath.swift

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+func breadthFirstSearchShortestPath(graph: Graph, source: Node) {
+  var queue = Queue<Node>()
+  queue.enqueue(source)
+  source.distance = 0
+
+  while !queue.isEmpty {
+    let current = queue.dequeue()!
+    for edge in current.neighbors {
+      let neighborNode = edge.neighbor
+      if !neighborNode.hasDistance {
+        queue.enqueue(neighborNode)
+        neighborNode.distance = current.distance! + 1
+      }
+    }
+  }
+
+  print(graph.nodes)
+}

Breadth-First Search/Edge.swift

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+public class Edge {
+  public var neighbor: Node
+
+  public init(neighbor: Node) {
+    self.neighbor = neighbor
+  }
+}

Breadth-First Search/Graph.swift

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+public class Graph : CustomStringConvertible {
+  public private(set) var nodes: [Node]
+
+  public init() {
+    self.nodes = []
+  }
+
+  public func addNode(label: String) -> Node {
+    let node = Node(label: label)
+    nodes.append(node)
+    return node
+  }
+
+  public func addEdge(source: Node, neighbor: Node) {
+    let edge = Edge(neighbor: neighbor)
+    edge.neighbor = neighbor
+    source.neighbors.append(edge)
+  }
+
+  public var description: String {
+    var description = ""
+
+    for node in nodes {
+      if !node.neighbors.isEmpty {
+        description += "[node: \(node.label) edges: \(node.neighbors.map{ $0.neighbor.label})]"
+      }
+    }
+    return description
+  }
+
+  public func findNodeWithLabel(label: String) -> Node {
+    return nodes.filter{ $0.label == label }.first!
+  }
+
+  public func duplicate() -> Graph {
+    let duplicated = Graph()
+
+    for node in nodes {
+      duplicated.addNode(node.label)
+    }
+
+    for node in nodes {
+      for edge in node.neighbors {
+        let source = duplicated.findNodeWithLabel(node.label)
+        let neighbour = duplicated.findNodeWithLabel(edge.neighbor.label)
+        duplicated.addEdge(source, neighbor: neighbour)
+      }
+    }
+
+    return duplicated
+  }
+}

Breadth-First Search/Node.swift

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+public class Node : CustomStringConvertible, Equatable {
+  public var neighbors: [Edge]
+  
+  public private(set) var label: String
+  public var distance: Int?
+  public var visited: Bool
+
+  public init(label: String) {
+    self.label = label
+    neighbors = []
+    visited = false
+  }
+
+  public var description: String {
+    if let distance = distance {
+      return "Node(label: \(label), distance: \(distance))"
+    }
+    return "Node(label: \(label), distance: infinity)"
+  }
+
+  public var hasDistance: Bool {
+    return distance != nil
+  }
+
+  public func remove(edge: Edge) {
+    neighbors.removeAtIndex(neighbors.indexOf{ $0 === edge }!)
+  }
+}
+
+public func ==(lhs: Node, rhs: Node) -> Bool {
+  return lhs.label == rhs.label
+}

Breadth-First Search/Queue.swift

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+public struct Queue<T> {
+  private var array: [T]
+
+  public init() {
+    array = []
+  }
+
+  public var isEmpty: Bool {
+    return array.isEmpty
+  }
+
+  public var count: Int {
+    return array.count
+  }
+
+  public mutating func enqueue(element: T) {
+    array.append(element)
+  }
+
+  public mutating func dequeue() -> T? {
+    if isEmpty {
+      return nil
+    } else {
+      return array.removeFirst()
+    }
+  }
+
+  public func peek() -> T? {
+    return array.first
+  }
+}

Breadth-First Search/Tests/BreadthFirstSearchTests.swift

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+import Foundation
+import XCTest
+
+class QueueTest: XCTestCase {
+  func testFail() {
+    XCTAssertFalse(true)
+  }
+}

Breadth-First Search/Tests/Info.plist

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+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>CFBundleDevelopmentRegion</key>
+	<string>en</string>
+	<key>CFBundleExecutable</key>
+	<string>$(EXECUTABLE_NAME)</string>
+	<key>CFBundleIdentifier</key>
+	<string>$(PRODUCT_BUNDLE_IDENTIFIER)</string>
+	<key>CFBundleInfoDictionaryVersion</key>
+	<string>6.0</string>
+	<key>CFBundleName</key>
+	<string>$(PRODUCT_NAME)</string>
+	<key>CFBundlePackageType</key>
+	<string>BNDL</string>
+	<key>CFBundleShortVersionString</key>
+	<string>1.0</string>
+	<key>CFBundleSignature</key>
+	<string>????</string>
+	<key>CFBundleVersion</key>
+	<string>1</string>
+</dict>
+</plist>