Added reversed graph and tests

Author: mattpaletta

Sources/SwiftGraph/Graph.swift

@@ -244,6 +244,17 @@ extension Graph {
     public func edgeExists(_ edge: E) -> Bool {
         return edges[edge.u].contains(edge)
     }
+    
+    /// Returns a graph of the same type with all edges reversed.
+    ///
+    /// - returns: Graph of the same type with all edges reversed.
+    public func reversed() -> Self {
+        let g = Self(vertices: self.vertices)
+        for e in self.edgeList() {
+            g.addEdge(e.reversed(), directed: e.directed)
+        }
+        return g
+    }
 
 
     // MARK: Implement Printable protocol

Tests/SwiftGraphTests/SwiftGraphSortTests.swift

@@ -23,6 +23,25 @@ class SwiftGraphSortTests: XCTestCase {
     // pg 1016 Liang
     let dressDAG: UnweightedGraph<String> = UnweightedGraph<String>(vertices: ["undershorts", "socks", "pants", "shoes", "watch", "belt", "shirt", "tie", "jacket"])
 
+    private func comesBefore<T: Equatable>(order: [T], a: T, b: T) -> Bool {
+        let aPos = order.firstIndex { (i) -> Bool in
+            return i == a
+        }
+        let bPos = order.firstIndex { (i) -> Bool in
+            return i == b
+        }
+        
+        guard let A = aPos, let B = bPos else { return false }
+        return A < B
+    }
+    
+    func testComesBefore() {
+        XCTAssertTrue(comesBefore(order: [5, 4, 3, 2, 1], a: 3, b: 1))
+        XCTAssertTrue(comesBefore(order: [5, 4, 3, 2, 1], a: 5, b: 2))
+        XCTAssertTrue(comesBefore(order: ["A", "B", "C"], a: "A", b: "C"))
+
+    }
+    
     override func setUp() {
         super.setUp()
         // Put setup code here. This method is called before the invocation of each test method in the class.
@@ -56,5 +75,15 @@ class SwiftGraphSortTests: XCTestCase {
         }
         print(result)
         XCTAssertEqual(result.count, 9, "All items in sort.")
+        XCTAssertTrue(comesBefore(order: result, a: "undershorts", b: "shoes"))
+        XCTAssertTrue(comesBefore(order: result, a: "pants", b: "shoes"))
+        XCTAssertTrue(comesBefore(order: result, a: "socks", b: "shoes"))
+        XCTAssertTrue(comesBefore(order: result, a: "undershorts", b: "pants"))
+        XCTAssertTrue(comesBefore(order: result, a: "pants", b: "belt"))
+        XCTAssertTrue(comesBefore(order: result, a: "belt", b: "jacket"))
+        XCTAssertTrue(comesBefore(order: result, a: "shirt", b: "tie"))
+        XCTAssertTrue(comesBefore(order: result, a: "shirt", b: "belt"))
+        XCTAssertTrue(comesBefore(order: result, a: "tie", b: "jacket"))
+
     }
 }

Tests/SwiftGraphTests/SwiftGraphTests.swift

@@ -95,4 +95,44 @@ class SwiftGraphTests: XCTestCase {
         XCTAssertFalse(graph.edgeExists(fromIndex: 2, toIndex: 3))
         XCTAssertFalse(graph.edgeExists(fromIndex: 3, toIndex: 2))
     }
+    
+    func testCitesReversedDirected() {
+        let g = UnweightedGraph<String>(vertices: ["Atlanta", "New York", "Miami"])
+        g.addEdge(from: "Atlanta", to: "New York", directed: true)
+        g.addEdge(from: "Miami", to: "Atlanta", directed: true)
+        g.addEdge(from: "New York", to: "Miami", directed: true)
+        
+        XCTAssertTrue(g.edgeExists(from: "Atlanta", to: "New York"))
+        XCTAssertTrue(g.edgeExists(from: "Miami", to: "Atlanta"))
+        XCTAssertTrue(g.edgeExists(from: "New York", to: "Miami"))
+        
+        let r: UnweightedGraph<String> = g.reversed()
+        XCTAssertFalse(r.edgeExists(from: "Atlanta", to: "New York"))
+        XCTAssertFalse(r.edgeExists(from: "Miami", to: "Atlanta"))
+        XCTAssertFalse(r.edgeExists(from: "New York", to: "Miami"))
+        
+        XCTAssertTrue(r.edgeExists(from: "New York", to: "Atlanta"))
+        XCTAssertTrue(r.edgeExists(from: "Atlanta", to: "Miami"))
+        XCTAssertTrue(r.edgeExists(from: "Miami", to: "New York"))
+    }
+    
+    func testCitesReversedUndirected() {
+        let g = UnweightedGraph<String>(vertices: ["Atlanta", "New York", "Miami"])
+        g.addEdge(from: "Atlanta", to: "New York", directed: false)
+        g.addEdge(from: "Miami", to: "Atlanta", directed: false)
+        g.addEdge(from: "New York", to: "Miami", directed: false)
+        
+        XCTAssertTrue(g.edgeExists(from: "Atlanta", to: "New York"))
+        XCTAssertTrue(g.edgeExists(from: "Miami", to: "Atlanta"))
+        XCTAssertTrue(g.edgeExists(from: "New York", to: "Miami"))
+        
+        let r: UnweightedGraph<String> = g.reversed()
+        XCTAssertTrue(r.edgeExists(from: "Atlanta", to: "New York"))
+        XCTAssertTrue(r.edgeExists(from: "Miami", to: "Atlanta"))
+        XCTAssertTrue(r.edgeExists(from: "New York", to: "Miami"))
+        
+        XCTAssertTrue(r.edgeExists(from: "New York", to: "Atlanta"))
+        XCTAssertTrue(r.edgeExists(from: "Atlanta", to: "Miami"))
+        XCTAssertTrue(r.edgeExists(from: "Miami", to: "New York"))
+    }
 }