Add Dijkstra algorithm implementation and tests

graph/dijkstra.py

@@ -0,0 +1,49 @@
+from typing import Dict, List, Tuple
+import heapq
+
+def dijkstra(graph: Dict[int, List[Tuple[int, int]]], start: int) -> Dict[int, int]:
+    """
+    Implements Dijkstra's algorithm for finding the shortest path in a graph.
+
+    Args:
+    graph (Dict[int, List[Tuple[int, int]]]): A dictionary representing the graph.
+                                              Keys are nodes, values are lists of (neighbor, weight) tuples.
+    start (int): The starting node.
+
+    Returns:
+    Dict[int, int]: A dictionary with nodes as keys and shortest distances from start as values.
+    """
+    distances = {node: float('infinity') for node in graph}
+    distances[start] = 0
+    pq = [(0, start)]
+
+    while pq:
+        current_distance, current_node = heapq.heappop(pq)
+
+        if current_distance > distances[current_node]:
+            continue
+
+        for neighbor, weight in graph[current_node]:
+            distance = current_distance + weight
+            if distance < distances[neighbor]:
+                distances[neighbor] = distance
+                heapq.heappush(pq, (distance, neighbor))
+
+    return distances
+
+# Example usage
+if __name__ == "__main__":
+    # Example graph
+    graph = {
+        0: [(1, 4), (2, 1)],
+        1: [(3, 1)],
+        2: [(1, 2), (3, 5)],
+        3: [(4, 3)],
+        4: []
+    }
+
+    start_node = 0
+    shortest_paths = dijkstra(graph, start_node)
+    print(f"Shortest paths from node {start_node}:")
+    for node, distance in shortest_paths.items():
+        print(f"To node {node}: {distance}")

graph/test_dijkstra.py

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+import unittest
+from dijkstra import dijkstra
+
+class TestDijkstra(unittest.TestCase):
+    def test_simple_graph(self):
+        graph = {
+            0: [(1, 4), (2, 1)],
+            1: [(3, 1)],
+            2: [(1, 2), (3, 5)],
+            3: [(4, 3)],
+            4: []
+        }
+        start_node = 0
+        expected = {0: 0, 1: 3, 2: 1, 3: 4, 4: 7}
+        self.assertEqual(dijkstra(graph, start_node), expected)
+
+    def test_disconnected_graph(self):
+        graph = {
+            0: [(1, 1)],
+            1: [(0, 1)],
+            2: [(3, 1)],
+            3: [(2, 1)]
+        }
+        start_node = 0
+        expected = {0: 0, 1: 1, 2: float('infinity'), 3: float('infinity')}
+        self.assertEqual(dijkstra(graph, start_node), expected)
+
+    def test_single_node_graph(self):
+        graph = {0: []}
+        start_node = 0
+        expected = {0: 0}
+        self.assertEqual(dijkstra(graph, start_node), expected)
+
+    def test_complex_graph(self):
+        graph = {
+            0: [(1, 4), (2, 2)],
+            1: [(2, 1), (3, 5)],
+            2: [(3, 8), (4, 10)],
+            3: [(4, 2), (5, 6)],
+            4: [(5, 3)],
+            5: []
+        }
+        start_node = 0
+        expected = {0: 0, 1: 4, 2: 2, 3: 9, 4: 11, 5: 14}
+        self.assertEqual(dijkstra(graph, start_node), expected)
+
+    def test_start_node_not_in_graph(self):
+        graph = {0: [(1, 1)], 1: [(0, 1)]}
+        start_node = 2
+        with self.assertRaises(KeyError):
+            dijkstra(graph, start_node)
+
+if __name__ == '__main__':
+    unittest.main()