From 049884f440aa0456ee2600b6f3222ab53a9600f5 Mon Sep 17 00:00:00 2001
From: TizianoCoroneo <tizianocoroneo@me.com>
Date: Sun, 5 May 2024 00:39:00 +0200
Subject: [PATCH] feat: indegree and outdegree functions

---
 Sources/SwiftGraph/Graph.swift              | 22 ++++++++++++
 Tests/SwiftGraphTests/SwiftGraphTests.swift | 39 ++++++++++++++++++++-
 2 files changed, 60 insertions(+), 1 deletion(-)

diff --git a/Sources/SwiftGraph/Graph.swift b/Sources/SwiftGraph/Graph.swift
index 4dcf770..575d6fe 100644
--- a/Sources/SwiftGraph/Graph.swift
+++ b/Sources/SwiftGraph/Graph.swift
@@ -236,6 +236,28 @@ extension Graph {
             removeVertexAtIndex(i)
         }
     }
+    
+    /// How many edges end at the vertex at this index? Undirected edges are considered as ending at both vertices.
+    ///
+    /// - Parameter index: Index of the vertex.
+    /// - Returns: The count of edges that end at that vertex.
+    public func indegreeOfVertex(at index: Int) -> Int {
+        var count = 0
+        for edgesForVertex in edges {
+            for edge in edgesForVertex where edge.v == index {
+                count += 1
+            }
+        }
+        return count
+    }
+
+    /// How many edges start at the vertex at this index? Undirected edges are considered as starting at both vertices.
+    ///
+    /// - Parameter index: Index of the vertex.
+    /// - Returns: The count of edges that start at that vertex.
+    public func outdegreeOfVertex(at index: Int) -> Int {
+        edges[index].count
+    }
 
     /// Check whether an edge is in the graph or not.
     ///
diff --git a/Tests/SwiftGraphTests/SwiftGraphTests.swift b/Tests/SwiftGraphTests/SwiftGraphTests.swift
index 114d987..55a28ca 100644
--- a/Tests/SwiftGraphTests/SwiftGraphTests.swift
+++ b/Tests/SwiftGraphTests/SwiftGraphTests.swift
@@ -71,7 +71,44 @@ class SwiftGraphTests: XCTestCase {
         XCTAssertEqual(g.vertexCount, 2, "2 total vertices")
         XCTAssertEqual(g.edgeCount, 1, "1 total edges")
     }
-    
+
+    func testIndegreeAndOutdegree() {
+        var g = UnweightedGraph<String>()
+        let atlantaIndex = g.addVertex("Atlanta")
+        let nyIndex = g.addVertex("New York")
+        let miamiIndex = g.addVertex("Miami")
+        let sfIndex = g.addVertex("San Francisco")
+        let arezzoIndex = g.addVertex("Arezzo")
+        g.addEdge(from: "Atlanta", to: "New York", directed: true)
+        let nyAtlantaEdge = UnweightedEdge(u: nyIndex, v: atlantaIndex, directed: true)
+        g.addEdge(nyAtlantaEdge, directed: true)
+        g.addEdge(from: "Miami", to: "Atlanta", directed: true)
+        g.addEdge(from: "New York", to: "Miami", directed: false)
+        g.addEdge(from: "Atlanta", to: "Miami", directed: true)
+        g.addEdge(from: "San Francisco", to: "Miami", directed: false)
+        XCTAssertEqual(g.indegreeOfVertex(at: atlantaIndex), 2, "2 edges end at Atlanta")
+        XCTAssertEqual(g.indegreeOfVertex(at: miamiIndex), 3, "3 edges end at Miami")
+        XCTAssertEqual(g.indegreeOfVertex(at: sfIndex), 1, "1 edge ends at San Francisco")
+        XCTAssertEqual(g.indegreeOfVertex(at: nyIndex), 2, "2 edges end at New York")
+        XCTAssertEqual(g.indegreeOfVertex(at: arezzoIndex), 0, "0 edges end at Arezzo")
+        XCTAssertEqual(g.outdegreeOfVertex(at: atlantaIndex), 2, "2 edges start from Atlanta")
+        XCTAssertEqual(g.outdegreeOfVertex(at: miamiIndex), 3, "3 edges start from Miami")
+        XCTAssertEqual(g.outdegreeOfVertex(at: sfIndex), 1, "1 edge starts from San Francisco")
+        XCTAssertEqual(g.outdegreeOfVertex(at: nyIndex), 2, "2 edges start from New York")
+        XCTAssertEqual(g.outdegreeOfVertex(at: arezzoIndex), 0, "0 edges start from Arezzo")
+        g.removeEdge(nyAtlantaEdge)
+        XCTAssertEqual(g.indegreeOfVertex(at: atlantaIndex), 1, "1 edgee ends at Atlanta")
+        XCTAssertEqual(g.indegreeOfVertex(at: miamiIndex), 3, "3 edges end at Miami")
+        XCTAssertEqual(g.indegreeOfVertex(at: sfIndex), 1, "1 edge ends at San Francisco")
+        XCTAssertEqual(g.indegreeOfVertex(at: nyIndex), 2, "2 edges end at New York")
+        XCTAssertEqual(g.indegreeOfVertex(at: arezzoIndex), 0, "0 edges end at Arezzo")
+        XCTAssertEqual(g.outdegreeOfVertex(at: atlantaIndex), 2, "2 edges start from Atlanta")
+        XCTAssertEqual(g.outdegreeOfVertex(at: miamiIndex), 3, "3 edges start from Miami")
+        XCTAssertEqual(g.outdegreeOfVertex(at: sfIndex), 1, "1 edge starts from San Francisco")
+        XCTAssertEqual(g.outdegreeOfVertex(at: nyIndex), 1, "1 edge starts from New York")
+        XCTAssertEqual(g.outdegreeOfVertex(at: arezzoIndex), 0, "0 edges start from Arezzo")
+    }
+
     func testSubscript() {
         let g: UnweightedGraph<String> = UnweightedGraph<String>()
         _ = g.addVertex("Atlanta")