RecursionUtils methods for finding a path in a graph

ICD.Common.Utils/RecursionUtils.cs

@@ -1,5 +1,7 @@
 using System;
 using System.Collections.Generic;
+using System.Linq;
+using ICD.Common.Properties;
 
 namespace ICD.Common.Utils
 {
@@ -14,6 +16,9 @@ namespace ICD.Common.Utils
 		/// <returns></returns>
 		public static IEnumerable<T> BreadthFirstSearch<T>(T root, Func<T, IEnumerable<T>> getChildren)
 		{
+			if (getChildren == null)
+				throw new ArgumentNullException("getChildren");
+
 			Queue<T> process = new Queue<T>();
 			process.Enqueue(root);
 
@@ -26,5 +31,84 @@ namespace ICD.Common.Utils
 					process.Enqueue(child);
 			}
 		}
+
+		/// <summary>
+		/// Returns the shortest path from root to destination via breadth-first search.
+		/// </summary>
+		/// <typeparam name="T"></typeparam>
+		/// <param name="root"></param>
+		/// <param name="destination"></param>
+		/// <param name="getChildren"></param>
+		/// <returns></returns>
+		[CanBeNull]
+		public static IEnumerable<T> BreadthFirstSearchPath<T>(T root, T destination, Func<T, IEnumerable<T>> getChildren)
+		{
+			if (getChildren == null)
+				throw new ArgumentNullException("getChildren");
+
+			return BreadthFirstSearchPath(root, destination, getChildren, EqualityComparer<T>.Default);
+		}
+
+		/// <summary>
+		/// Returns the shortest path from root to destination via breadth-first search.
+		/// </summary>
+		/// <typeparam name="T"></typeparam>
+		/// <param name="root"></param>
+		/// <param name="destination"></param>
+		/// <param name="getChildren"></param>
+		/// <param name="comparer"></param>
+		/// <returns></returns>
+		[CanBeNull]
+		public static IEnumerable<T> BreadthFirstSearchPath<T>(T root, T destination, Func<T, IEnumerable<T>> getChildren,
+		                                                       IEqualityComparer<T> comparer)
+		{
+			if (getChildren == null)
+				throw new ArgumentNullException("getChildren");
+
+			if (comparer == null)
+				throw new ArgumentNullException("comparer");
+
+			Queue<T> queue = new Queue<T>();
+			queue.Enqueue(root);
+
+			Dictionary<T, T> nodeParents = new Dictionary<T, T>();
+
+			while (queue.Count > 0)
+			{
+				T current = queue.Dequeue();
+
+				foreach (T node in getChildren(current))
+				{
+					if (nodeParents.ContainsKey(node))
+						continue;
+
+					queue.Enqueue(node);
+					nodeParents.Add(node, current);
+
+					// Found a path to the destination
+					if (comparer.Equals(node, destination))
+						return GetPath(destination, nodeParents).Reverse();
+				}
+			}
+
+			return null;
+		}
+
+		/// <summary>
+		/// Walks through a map of nodes from the starting point.
+		/// </summary>
+		/// <typeparam name="T"></typeparam>
+		/// <param name="start"></param>
+		/// <param name="nodeParents"></param>
+		/// <returns></returns>
+		private static IEnumerable<T> GetPath<T>(T start, IDictionary<T, T> nodeParents)
+		{
+			while (true)
+			{
+				yield return start;
+				if (!nodeParents.TryGetValue(start, out start))
+					break;
+			}
+		}
 	}
 }