Create graphs/dijkstra_alternate.py (TheAlgorithms#7405)

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Co-authored-by: Christian Clauss <[email protected]>

* Update graphs/dijkstra.py

Co-authored-by: Christian Clauss <[email protected]>

* Update graphs/dijkstra.py

Co-authored-by: Christian Clauss <[email protected]>

* Update dijkstra.py

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* Create dijkstra_alternate.py

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* int(1e7)

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* sptset --> visited

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Co-authored-by: Christian Clauss <[email protected]>

Author: 3 people

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)