Merge pull request #41 from 5sw/graphs

Depth-first and breadth-first search in graphs

DIRECTORY.md

@@ -55,6 +55,7 @@
  * [Union Find](https://github.com/TheAlgorithms/Swift/blob/master/data_structures/union_find/union_find.swift)
 
 ## Graph
+ * [Graph](https://github.com/TheAlgorithms/Swift/blob/master/graph/Graph.swift)
  * Bfs
  * [Bfs](https://github.com/TheAlgorithms/Swift/blob/master/graph/BFS/BFS.swift)
  * Dfs

graph/Graph.swift

@@ -0,0 +1,109 @@
+struct GraphEdge<G: Graph> {
+ var from: G.Node
+ var to: G.Node
+ var value: G.EdgeValue
+}
+
+protocol Graph {
+ typealias Edge = GraphEdge<Self>
+
+ associatedtype Node: Equatable
+ associatedtype EdgeValue
+
+ func edges(from: Node) -> [Edge]
+}
+
+struct AdjacencyList<Node: Hashable, EdgeValue>: Graph {
+ typealias EdgeValue = EdgeValue
+ typealias Node = Node
+
+ var graph: [Node: [Edge]] = [:]
+
+ func edges(from node: Node) -> [Edge] {
+ graph[node, default: []]
+ }
+
+ mutating func insert(from: Node, to: Node, value: EdgeValue) {
+ graph[from, default: []].append(Edge(from: from, to: to, value: value))
+ }
+
+ var allEdges: [Edge] {
+ graph.values.flatMap { $0 }
+ }
+}
+
+extension AdjacencyList where EdgeValue == () {
+ mutating func insert(from: Node, to: Node) {
+ insert(from: from, to: to, value: ())
+ }
+}
+
+extension Graph {
+ func depthFirstSearch(start: Node, destination: Node) -> [Edge]? {
+ if start == destination {
+ return []
+ }
+
+ for edge in edges(from: start) {
+ if let path = depthFirstSearch(start: edge.to, destination: destination) {
+ return [edge] + path
+ }
+ }
+
+ return nil
+ }
+}
+
+extension Graph where Node: Hashable {
+ func breadthFirstSearch(start: Node, destination: Node) -> [Edge]? {
+ var queue: [(Node, [Edge])] = [(start, [])]
+ var visited: Set<Node> = [start]
+
+ while !queue.isEmpty {
+ let (current, path) = queue.removeFirst()
+ if current == destination {
+ return path
+ }
+
+ for edge in edges(from: current) where visited.insert(edge.to).inserted {
+ queue.append((edge.to, path + [edge]))
+ }
+ }
+
+ return nil
+ }
+}
+
+extension GraphEdge: CustomDebugStringConvertible {
+ var debugDescription: String {
+ if type(of: value) == Void.self {
+ return "\(from) -- \(to)"
+ } else {
+ return "\(from) -\(value)- \(to)"
+ }
+ }
+}
+
+var graph = AdjacencyList<String, Void>()
+graph.insert(from: "a", to: "b")
+graph.insert(from: "a", to: "d")
+graph.insert(from: "b", to: "c")
+graph.insert(from: "c", to: "d")
+
+func test<G: Graph>(_ message: String, _ list: [GraphEdge<G>]?) {
+ print(message)
+ if let list = list {
+ for edge in list {
+ print(edge)
+ }
+ } else {
+ print("Not found")
+ }
+ print("")
+}
+
+test("Depth-first a -> d", graph.depthFirstSearch(start: "a", destination: "d"))
+test("Depth-first a -> e", graph.depthFirstSearch(start: "a", destination: "e"))
+
+test("Breadth-first a -> d", graph.breadthFirstSearch(start: "a", destination: "d"))
+test("Breadth-first a -> e", graph.breadthFirstSearch(start: "a", destination: "e"))