diff --git a/Prims_algorithm.py b/Prims_algorithm.py new file mode 100644 index 00000000..3aa8ad20 --- /dev/null +++ b/Prims_algorithm.py @@ -0,0 +1,96 @@ +# A Python implementation of +# Prim's Minimum Spanning Tree (MST) algorithm. +# The program is for an adjacency matrix +# representation of the graph. Time +# Time complexity is O(V^2). If the input +# graph is represented as an adjacency list +# rather than a matrix, time complexity +# can be reduced O(E * logV) with the help of +# a binary heap. Space complexity: O(V). + + +import sys + + +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): + + # Initialize min value + min = sys.maxsize + + 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.maxsize] * 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 shortest 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) + + +# Driver's code +if __name__ == '__main__': + 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() + + +