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Deepali-SrivastavaDeepali-Srivastava
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Kruskal’s algorithm in Python
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‎Graph/kruskals-algorithm.py

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# Copyright (C) Deepali Srivastava - All Rights Reserved
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# This code is part of DSA course available on CourseGalaxy.com
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class Vertex:
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def __init__(self, name):
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self.name = name
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class UndirectedWeightedGraph:
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def __init__(self,size=20):
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self._adj = [ [0 for column in range(size)] for row in range(size) ]
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self._n = 0
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self._vertexList = []
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def display(self):
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for i in range(self._n):
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for j in range(self._n):
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print( self._adj[i][j], end =' ')
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print()
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def numVertices(self):
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return self._n
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def numEdges(self):
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e = 0
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for i in range(self._n):
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for j in range(i):
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if self._adj[i][j]!=0:
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e+=1
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return e
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def vertices(self):
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return [vertex.name for vertex in self._vertexList]
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def edges(self):
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edges = []
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for i in range(self._n):
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for j in range(i):
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if self._adj[i][j] != 0:
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edges.append( (self._vertexList[i].name, self._vertexList[j].name, self._adj[i][j]) )
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return edges
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def _getIndex(self,s):
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index = 0
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for name in (vertex.name for vertex in self._vertexList):
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if s == name:
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return index
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index += 1
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return None
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def insertVertex(self,name):
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if name in (vertex.name for vertex in self._vertexList): ########
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print("Vertex with this name already present in the graph")
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return
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self._vertexList.append( Vertex(name) )
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self._n += 1
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def removeVertex(self,name):
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u = self._getIndex(name)
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if u is None:
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print("Vertex not present in the graph")
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return
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self._adj.pop(u)
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for i in range(self._n):
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self._adj[i].pop(u)
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self._vertexList.pop(u)
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self._n -= 1
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def insertEdge(self, s1, s2, w):
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u = self._getIndex(s1)
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v = self._getIndex(s2)
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if u is None:
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print("First vertex not present in the graph")
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elif v is None:
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print("Second vertex not present in the graph")
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elif u == v:
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print("Not a valid edge")
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elif self._adj[u][v] != 0 :
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print("Edge already present in the graph")
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else:
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self._adj[u][v] = w
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self._adj[v][u] = w
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def removeEdge(self, s1,s2):
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u = self._getIndex(s1)
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v = self._getIndex(s2)
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if u is None:
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print("First vertex not present in the graph")
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elif v is None:
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print("Second vertex not present in the graph")
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elif self._adj[u][v] == 0:
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print("Edge not present in the graph")
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else:
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self._adj[u][v] = 0
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self._adj[v][u] = 0
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def isAdjacent(self, s1, s2):
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u = self._getIndex(s1)
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v = self._getIndex(s2)
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if u is None:
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print("First vertex not present in the graph")
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return False
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elif v is None:
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print("Second vertex not present in the graph")
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return False
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return False if self._adj[u][v] == 0 else True
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def degree(self,s):
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u = self._getIndex(s)
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if u is None:
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print("Vertex not present in the graph")
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return
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deg = 0
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for v in range(self._n):
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if self._adj[u][v] != 0 :
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deg += 1
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return deg
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def kruskals(self):
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edgesList = []
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for u in range(self._n):
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for v in range(self._n):
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if self._adj[u][v] != 0:
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edgesList.append( (u,v,self._adj[u][v]) )
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edgesList = sorted(edgesList, key = lambda item: item[2], reverse = True)
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for v in range(self._n):
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self._vertexList[v].father = None
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r1 = None
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r2 = None
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edgesInTree = 0
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wtTree = 0
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while len(edgesList)!=0 and edgesInTree < self._n-1 :
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edge = edgesList.pop()
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v1 = edge[0]
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v2 = edge[1]
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v = v1
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while self._vertexList[v].father != None :
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v = self._vertexList[v].father
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r1 = v
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v = v2
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while self._vertexList[v].father!=None :
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v = self._vertexList[v].father
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r2 = v
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if r1 != r2 : #Edge (v1,v2) is included
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edgesInTree += 1
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print(self._vertexList[v1].name , "->" , self._vertexList[v2].name )
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wtTree += edge[2]
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self._vertexList[r2].father = r1
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if edgesInTree < self._n-1:
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print("Graph is not connected, no spanning tree possible")
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return
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print("Weight of Minimum Spanning Tree is " , wtTree)
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if __name__ == '__main__':
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g = UndirectedWeightedGraph()
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g.insertVertex("Zero")
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g.insertVertex("One")
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g.insertVertex("Two")
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g.insertVertex("Three")
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g.insertVertex("Four")
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g.insertVertex("Five")
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g.insertVertex("Six")
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g.insertVertex("Seven")
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g.insertVertex("Eight")
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g.insertVertex("Nine")
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g.insertEdge("Zero", "One", 19)
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g.insertEdge("Zero", "Three", 14)
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g.insertEdge("Zero", "Four", 12)
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g.insertEdge("One", "Two", 20)
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g.insertEdge("One", "Four", 18)
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g.insertEdge("Two", "Four", 17)
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g.insertEdge("Two", "Five", 15)
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g.insertEdge("Two", "Nine", 29)
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g.insertEdge("Three", "Four", 13)
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g.insertEdge("Three", "Six", 28)
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g.insertEdge("Four", "Five", 16)
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g.insertEdge("Four", "Six", 21)
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g.insertEdge("Four", "Seven", 22)
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g.insertEdge("Four", "Eight", 24)
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g.insertEdge("Five", "Eight", 26)
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g.insertEdge("Five", "Nine", 27)
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g.insertEdge("Six", "Seven", 23)
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g.insertEdge("Seven", "Eight", 30)
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g.insertEdge("Eight", "Nine", 35)
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g.kruskals()

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