From 7b08311b01bb7f4f2a261286e93e9cf7abe6da1b Mon Sep 17 00:00:00 2001
From: Robert Manson <robmanson@gmail.com>
Date: Sun, 3 Nov 2019 17:36:22 -0800
Subject: [PATCH] Fix infinite recursion in DFS

Fixes infinite recursion in the DFS algorithm for topological sort caused by graphs with cycles.
For example the following graph would previously have recursed indefinitely `a->b->a`.
---
 Topological Sort/TopologicalSort1.swift | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Topological Sort/TopologicalSort1.swift b/Topological Sort/TopologicalSort1.swift
index 2ad9b51a0..05f1ab887 100644
--- a/Topological Sort/TopologicalSort1.swift	
+++ b/Topological Sort/TopologicalSort1.swift	
@@ -1,6 +1,7 @@
 extension Graph {
   private func depthFirstSearch(_ source: Node, visited: inout [Node : Bool]) -> [Node] {
     var result = [Node]()
+    visited[source] = true
 
     if let adjacencyList = adjacencyList(forNode: source) {
       for nodeInAdjacencyList in adjacencyList {
@@ -10,7 +11,6 @@ extension Graph {
       }
     }
 
-    visited[source] = true
     return [source] + result
   }