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Commit 37bf8d4

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Dijkstra’s Algorithm in Python
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‎Graph/dijkstras-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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from sys import maxsize as INFINITY
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TEMPORARY = 1
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PERMANENT = 2
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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 DirectedWeightedGraph:
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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(self._n):
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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(self._n):
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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("Start vertex not present in the graph, first insert the start vertex")
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elif v is None:
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print("End vertex not present in the graph, first insert the end vertex")
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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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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("Start vertex not present in the graph ")
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elif v is None:
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print("End 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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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("Start 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("End 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 outdegree(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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outd = 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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outd+=1
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return outd
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def indegree(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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ind = 0
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for v in range(self._n):
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if self._adj[v][u] !=0 :
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ind+=1
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return ind
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def _dijkstra(self, s):
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for v in range(self._n):
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self._vertexList[v].status = TEMPORARY
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self._vertexList[v].pathLength = INFINITY
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self._vertexList[v].predecessor = None
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self._vertexList[s].pathLength = 0
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while True:
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c = self._tempVertexMinPL()
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if c == None:
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return
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self._vertexList[c].status = PERMANENT
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for v in range(self._n):
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if self._adj[c][v]!=0 and self._vertexList[v].status == TEMPORARY:
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if self._vertexList[c].pathLength + self._adj[c][v] < self._vertexList[v].pathLength:
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self._vertexList[v].predecessor = c
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self._vertexList[v].pathLength = self._vertexList[c].pathLength + self._adj[c][v]
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def _tempVertexMinPL(self):
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min = INFINITY
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x = None
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for v in range(self._n):
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if self._vertexList[v].status == TEMPORARY and self._vertexList[v].pathLength < min:
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min = self._vertexList[v].pathLength
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x = v
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return x
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def findPaths(self, source):
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s = self._getIndex(source)
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if s is None:
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print("Vertex not present in the graph")
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return
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self._dijkstra(s)
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print("Source Vertex :", source)
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for v in range(self._n):
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print("Destination Vertex :", self._vertexList[v].name)
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if self._vertexList[v].pathLength == INFINITY :
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print("There is no path from ", source , "to vertex", self._vertexList[v].name, "\n")
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else:
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self._findPath(s,v)
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def _findPath(self, s, v):
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path = []
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sd = 0
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count = 0
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while v != s:
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count += 1
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path.append(v)
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u = self._vertexList[v].predecessor
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sd += self._adj[u][v]
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v = u
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path.append(s)
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print("Shortest Path is : ", end = " ")
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for u in reversed(path):
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print(u, end = " ")
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print("\nShortest distance is :", sd, "\n")
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if __name__ == '__main__':
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g = DirectedWeightedGraph()
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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.insertEdge("Zero", "Three", 2)
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g.insertEdge("Zero", "One", 5)
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g.insertEdge("Zero", "Four", 8)
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g.insertEdge("One", "Four", 2)
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g.insertEdge("Two", "One", 3)
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g.insertEdge("Two", "Five", 4)
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g.insertEdge("Three", "Four", 7)
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g.insertEdge("Three", "Six", 8)
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g.insertEdge("Four", "Five", 9)
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g.insertEdge("Four", "Seven", 4)
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g.insertEdge("Five", "One", 6)
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g.insertEdge("Six", "Seven", 9)
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g.insertEdge("Seven", "Three", 5)
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g.insertEdge("Seven", "Five", 3)
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g.insertEdge("Seven", "Eight", 5)
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g.insertEdge("Eight", "Five", 3)
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g.findPaths("Zero")
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