Add problem 743 - Network Delay Time

Author: anirudhology

problems/graph/network_delay_time.py

@@ -0,0 +1,29 @@
+import heapq
+from collections import defaultdict
+from typing import List
+
+
+class NetworkDelayTime:
+    @staticmethod
+    def networkDelayTime(times: List[List[int]], n: int, k: int) -> int:
+        # Dictionary to represent graph
+        graph = defaultdict(list)
+        for u, v, w in times:
+            graph[u].append((v, w))
+        # Set to store visited nodes
+        visited = set()
+        # Min heap
+        min_heap = [(0, k)]
+        # Process all nodes in the heap
+        while min_heap:
+            travel_time, node = heapq.heappop(min_heap)
+            visited.add(node)
+
+            if len(visited) == n:
+                return travel_time
+
+            for neighbor, time in graph[node]:
+                if neighbor not in visited:
+                    heapq.heappush(min_heap, (travel_time + time, neighbor))
+
+        return -1

tests/graph/network_delay_time_test.py

@@ -0,0 +1,32 @@
+import unittest
+
+from problems.graph.network_delay_time import NetworkDelayTime
+
+
+class TestNetworkDelayTime(unittest.TestCase):
+
+    def setUp(self):
+        self.network_delay_time = NetworkDelayTime()
+
+    def test_network_delay_time(self):
+        # Test case 1: Basic case with all nodes reachable
+        self.assertEqual(self.network_delay_time.networkDelayTime([[2, 1, 1], [2, 3, 1], [3, 4, 1]], 4, 2), 2)
+
+        # Test case 2: Node unreachable
+        self.assertEqual(self.network_delay_time.networkDelayTime([[1, 2, 1]], 2, 1), 1)
+
+        # Test case 3: Single node, self delay is 0
+        self.assertEqual(self.network_delay_time.networkDelayTime([], 1, 1), 0)
+
+        # Test case 4: All nodes connected in a line
+        self.assertEqual(self.network_delay_time.networkDelayTime([[1, 2, 1], [2, 3, 1], [3, 4, 1]], 4, 1), 3)
+
+        # Test case 5: Empty times array, unreachable nodes
+        self.assertEqual(self.network_delay_time.networkDelayTime([], 2, 1), -1)
+
+        # Test case 6: Cycle in the graph
+        self.assertEqual(self.network_delay_time.networkDelayTime([[1, 2, 1], [2, 3, 2], [3, 1, 3]], 3, 1), 3)
+
+
+if __name__ == '__main__':
+    unittest.main()