Breadth First Search

Author: ivanmmarkovic

Ch07. Graphs and Graph Algorithms/Breadth First Search/Queue.py

@@ -0,0 +1,17 @@
+
+
+class Queue:
+    def __init__(self):
+        self.queue = []
+
+    def enqueue(self, item):
+        self.queue.insert(0, item)
+
+    def dequeue(self):
+        return self.queue.pop()
+
+    def size(self):
+        return len(self.queue)
+
+    def isEmpty(self):
+        return self.queue == []

Ch07. Graphs and Graph Algorithms/Breadth First Search/breadth-first-search.py

@@ -0,0 +1,76 @@
+from Queue import Queue
+
+class Graph:
+    def __init__(self):
+        self.vertices = []
+        self.adjacencyList = {}
+        self.distance = {}
+        self.previous = {}
+
+    def add_vertex(self, v):
+        self.vertices.append(v)
+        self.adjacencyList[v] = []
+        self.distance[v] = 0
+        self.previous[v] = None
+
+    def add_edge(self,v1, v2):
+        self.adjacencyList[v1].append(v2)
+        self.adjacencyList[v2].append(v1)
+
+    def to_string(self):
+        result = ""
+        for vertex in self.vertices:
+            result += (vertex + " -> ")
+            for neighbour in self.adjacencyList[vertex]:
+                result += neighbour + " "
+            result += "\n"
+        return result
+
+    def breadth_first_search(self):
+        queue = Queue()
+        startVertex = self.vertices[0]
+        gray = [] # visited, not fully explored
+        black = [] # explored
+        gray.append(startVertex)
+        queue.enqueue(startVertex)
+        while not queue.isEmpty():
+            dequeued = queue.dequeue()
+            if dequeued not in black:
+                for neighbour in self.adjacencyList[dequeued]:
+                    if neighbour not in gray:
+                        queue.enqueue(neighbour)
+                        gray.append(neighbour)
+                        self.distance[neighbour] = self.distance[dequeued] + 1
+                        self.previous[neighbour] = dequeued
+            black.append(dequeued)
+            print("Explored " + dequeued, end = " ")
+        print("")
+
+    def showPath(self, vertex):
+        if self.previous[vertex] == None:
+            return vertex
+        else:
+            return self.showPath(self.previous[vertex]) + " -> " + vertex
+
+graph = Graph()
+
+
+vertices = ['A', 'B', 'C', 'D', 'E', 'F']
+# add vertices
+for i in range(len(vertices)):
+    graph.add_vertex(vertices[i])
+
+graph.add_edge('A', 'B')
+graph.add_edge('A', 'C')
+graph.add_edge('C', 'D')
+graph.add_edge('D', 'E')
+graph.add_edge('D', 'F')
+
+print(graph.to_string())
+print("##########################")
+graph.breadth_first_search()
+print(graph.distance)
+print(graph.previous)
+print(graph.showPath("F"))
+
+