iframe-proxy | Sunbelt Computer Software

History

111 lines (95 loc) · 3.6 KB

Raw

100

101

102

103

104

105

106

107

108

109

110

111

import sys

from collections import defaultdict

def PrimsAlgorithm(l):

nodePosition = []

def getPosition(vertex):

return nodePosition[vertex]

def setPosition(vertex, pos):

nodePosition[vertex] = pos

def topToBottom(heap, start, size, positions):

if start > size // 2 - 1:

return

else:

if 2 * start + 2 >= size:

m = 2 * start + 1

else:

if heap[2 * start + 1] < heap[2 * start + 2]:

m = 2 * start + 1

else:

m = 2 * start + 2

if heap[m] < heap[start]:

temp, temp1 = heap[m], positions[m]

heap[m], positions[m] = heap[start], positions[start]

heap[start], positions[start] = temp, temp1

temp = getPosition(positions[m])

setPosition(positions[m], getPosition(positions[start]))

setPosition(positions[start], temp)

topToBottom(heap, m, size, positions)

# Update function if value of any node in min-heap decreases

def bottomToTop(val, index, heap, position):

temp = position[index]

while(index != 0):

if index % 2 == 0:

parent = int( (index-2) / 2 )

else:

parent = int( (index-1) / 2 )

if val < heap[parent]:

heap[index] = heap[parent]

position[index] = position[parent]

setPosition(position[parent], index)

else:

heap[index] = val

position[index] = temp

setPosition(temp, index)

break

index = parent

else:

heap[0] = val

position[0] = temp

setPosition(temp, 0)

def heapify(heap, positions):

start = len(heap) // 2 - 1

for i in range(start, -1, -1):

topToBottom(heap, i, len(heap), positions)

def deleteMinimum(heap, positions):

temp = positions[0]

heap[0] = sys.maxsize

topToBottom(heap, 0, len(heap), positions)

return temp

visited = [0 for i in range(len(l))]

Nbr_TV = [-1 for i in range(len(l))] # Neighboring Tree Vertex of selected vertex

# Minimum Distance of explored vertex with neighboring vertex of partial tree formed in graph

Distance_TV = [] # Heap of Distance of vertices from their neighboring vertex

Positions = []

for x in range(len(l)):

p = sys.maxsize

Distance_TV.append(p)

Positions.append(x)

nodePosition.append(x)

TreeEdges = []

visited[0] = 1

Distance_TV[0] = sys.maxsize

for x in l[0]:

Nbr_TV[ x[0] ] = 0

Distance_TV[ x[0] ] = x[1]

heapify(Distance_TV, Positions)

for i in range(1, len(l)):

vertex = deleteMinimum(Distance_TV, Positions)

if visited[vertex] == 0:

TreeEdges.append((Nbr_TV[vertex], vertex))

visited[vertex] = 1

for v in l[vertex]:

if visited[v[0]] == 0 and v[1] < Distance_TV[ getPosition(v[0]) ]:

Distance_TV[ getPosition(v[0]) ] = v[1]

bottomToTop(v[1], getPosition(v[0]), Distance_TV, Positions)

Nbr_TV[ v[0] ] = vertex

return TreeEdges

# < --------- Prims Algorithm --------- >

n = int(input("Enter number of vertices: "))

e = int(input("Enter number of edges: "))

adjlist = defaultdict(list)

for x in range(e):

l = [int(x) for x in input().split()]

adjlist[l[0]].append([ l[1], l[2] ])

adjlist[l[1]].append([ l[0], l[2] ])

print(PrimsAlgorithm(adjlist))

Sunbelt Computer Software

PL/B Language Development and Support

Navigation Menu

Sunbelt Computer Software

PL/B Language Development and Support

FilesExpand file tree

minimum_spanning_tree_prims.py

Latest commit

History

minimum_spanning_tree_prims.py

File metadata and controls