diff --git a/graphs/dijkstra_alternate.py b/graphs/dijkstra_alternate.py new file mode 100644 index 000000000..7beef6b04 --- /dev/null +++ b/graphs/dijkstra_alternate.py @@ -0,0 +1,98 @@ +from __future__ import annotations + + +class Graph: + def __init__(self, vertices: int) -> None: + """ + >>> graph = Graph(2) + >>> graph.vertices + 2 + >>> len(graph.graph) + 2 + >>> len(graph.graph[0]) + 2 + """ + self.vertices = vertices + self.graph = [[0] * vertices for _ in range(vertices)] + + def print_solution(self, distances_from_source: list[int]) -> None: + """ + >>> Graph(0).print_solution([]) # doctest: +NORMALIZE_WHITESPACE + Vertex Distance from Source + """ + print("Vertex \t Distance from Source") + for vertex in range(self.vertices): + print(vertex, "\t\t", distances_from_source[vertex]) + + def minimum_distance( + self, distances_from_source: list[int], visited: list[bool] + ) -> int: + """ + A utility function to find the vertex with minimum distance value, from the set + of vertices not yet included in shortest path tree. + + >>> Graph(3).minimum_distance([1, 2, 3], [False, False, True]) + 0 + """ + + # Initialize minimum distance for next node + minimum = 1e7 + min_index = 0 + + # Search not nearest vertex not in the shortest path tree + for vertex in range(self.vertices): + if distances_from_source[vertex] < minimum and visited[vertex] is False: + minimum = distances_from_source[vertex] + min_index = vertex + return min_index + + def dijkstra(self, source: int) -> None: + """ + Function that implements Dijkstra's single source shortest path algorithm for a + graph represented using adjacency matrix representation. + + >>> Graph(4).dijkstra(1) # doctest: +NORMALIZE_WHITESPACE + Vertex Distance from Source + 0 10000000 + 1 0 + 2 10000000 + 3 10000000 + """ + + distances = [int(1e7)] * self.vertices # distances from the source + distances[source] = 0 + visited = [False] * self.vertices + + for _ in range(self.vertices): + u = self.minimum_distance(distances, visited) + visited[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.vertices): + if ( + self.graph[u][v] > 0 + and visited[v] is False + and distances[v] > distances[u] + self.graph[u][v] + ): + distances[v] = distances[u] + self.graph[u][v] + + self.print_solution(distances) + + +if __name__ == "__main__": + graph = Graph(9) + graph.graph = [ + [0, 4, 0, 0, 0, 0, 0, 8, 0], + [4, 0, 8, 0, 0, 0, 0, 11, 0], + [0, 8, 0, 7, 0, 4, 0, 0, 2], + [0, 0, 7, 0, 9, 14, 0, 0, 0], + [0, 0, 0, 9, 0, 10, 0, 0, 0], + [0, 0, 4, 14, 10, 0, 2, 0, 0], + [0, 0, 0, 0, 0, 2, 0, 1, 6], + [8, 11, 0, 0, 0, 0, 1, 0, 7], + [0, 0, 2, 0, 0, 0, 6, 7, 0], + ] + graph.dijkstra(0)