Create prims.py

Author: arnab132

prims.py

@@ -0,0 +1,81 @@
+# A Python program for Prim's Minimum Spanning Tree (MST) algorithm.
+
+# The program is for adjacency matrix representation of the graph
+
+import sys # Library for INT_MAX
+
+class Graph():
+
+	def __init__(self, vertices):
+		self.V = vertices
+		self.graph = [[0 for column in range(vertices)]
+					for row in range(vertices)]
+
+	# A utility function to print the constructed MST stored in parent[]
+	def printMST(self, parent):
+		print "Edge \tWeight"
+		for i in range(1, self.V):
+			print parent[i], "-", i, "\t", self.graph[i][ parent[i] ]
+
+	# A utility function to find the vertex with
+	# minimum distance value, from the set of vertices
+	# not yet included in shortest path tree
+	def minKey(self, key, mstSet):
+
+		# Initilaize min value
+		min = sys.maxint
+
+		for v in range(self.V):
+			if key[v] < min and mstSet[v] == False:
+				min = key[v]
+				min_index = v
+
+		return min_index
+
+	# Function to construct and print MST for a graph
+	# represented using adjacency matrix representation
+	def primMST(self):
+
+		# Key values used to pick minimum weight edge in cut
+		key = [sys.maxint] * self.V
+		parent = [None] * self.V # Array to store constructed MST
+		# Make key 0 so that this vertex is picked as first vertex
+		key[0] = 0
+		mstSet = [False] * self.V
+
+		parent[0] = -1 # First node is always the root of
+
+		for cout in range(self.V):
+
+			# Pick the minimum distance vertex from
+			# the set of vertices not yet processed.
+			# u is always equal to src in first iteration
+			u = self.minKey(key, mstSet)
+
+			# Put the minimum distance vertex in
+			# the shortest path tree
+			mstSet[u] = True
+
+			# Update dist value of the adjacent vertices
+			# of the picked vertex only if the current
+			# distance is greater than new distance and
+			# the vertex in not in the shotest path tree
+			for v in range(self.V):
+
+				# graph[u][v] is non zero only for adjacent vertices of m
+				# mstSet[v] is false for vertices not yet included in MST
+				# Update the key only if graph[u][v] is smaller than key[v]
+				if self.graph[u][v] > 0 and mstSet[v] == False and key[v] > self.graph[u][v]:
+						key[v] = self.graph[u][v]
+						parent[v] = u
+
+		self.printMST(parent)
+
+g = Graph(5)
+g.graph = [ [0, 2, 0, 6, 0],
+			[2, 0, 3, 8, 5],
+			[0, 3, 0, 0, 7],
+			[6, 8, 0, 0, 9],
+			[0, 5, 7, 9, 0]]
+
+g.primMST();