Add problem 787 - Cheapest Flights Within K Stops

Author: anirudhology

problems/graph/cheapest_flights_within_k_stops.py

@@ -0,0 +1,32 @@
+from collections import deque
+from typing import List
+
+
+class CheapestFlightsWithinKStops:
+    @staticmethod
+    def findCheapestPrice(n: int, flights: List[List[int]], src: int, dst: int, k: int) -> int:
+        # Adjacency list
+        graph = []
+        for i in range(n):
+            graph.append([])
+        for flight in flights:
+            graph[flight[0]].append([flight[1], flight[2]])
+        # Queue to perform BFS
+        nodes = deque([[src, 0]])
+        # Array to store minimum costs
+        min_cost = [0x7fffffff] * n
+        # Stops taken
+        stops = 0
+        # Process until queue is not empty and stops are less than equal to k
+        while nodes and stops <= k:
+            size = len(nodes)
+            for i in range(size):
+                current = nodes.popleft()
+                # Process the neighbors of this current node
+                for [node, cost] in graph[current[0]]:
+                    if (cost + current[1]) >= min_cost[node]:
+                        continue
+                    min_cost[node] = cost + current[1]
+                    nodes.append([node, min_cost[node]])
+            stops += 1
+        return min_cost[dst] if min_cost[dst] != 0x7fffffff else -1

tests/graph/cheapest_flights_within_k_stops_test.py

@@ -0,0 +1,60 @@
+import unittest
+
+from problems.graph.cheapest_flights_within_k_stops import CheapestFlightsWithinKStops
+
+
+class TestCheapestFlightsWithinKStops(unittest.TestCase):
+
+    def test_basic_scenario(self):
+        cheapest_flight_within_k_flights = CheapestFlightsWithinKStops()
+        n = 3
+        flights = [[0, 1, 100], [1, 2, 100], [0, 2, 500]]
+        src = 0
+        dst = 2
+        k = 1
+        result = cheapest_flight_within_k_flights.findCheapestPrice(n, flights, src, dst, k)
+        self.assertEqual(result, 200)
+
+    def test_no_available_flight(self):
+        cheapest_flight_within_k_flights = CheapestFlightsWithinKStops()
+        n = 3
+        flights = [[0, 1, 100]]
+        src = 0
+        dst = 2
+        k = 1
+        result = cheapest_flight_within_k_flights.findCheapestPrice(n, flights, src, dst, k)
+        self.assertEqual(result, -1)
+
+    def test_direct_flight(self):
+        cheapest_flight_within_k_flights = CheapestFlightsWithinKStops()
+        n = 3
+        flights = [[0, 2, 300]]
+        src = 0
+        dst = 2
+        k = 1
+        result = cheapest_flight_within_k_flights.findCheapestPrice(n, flights, src, dst, k)
+        self.assertEqual(result, 300)
+
+    def test_no_stop_allowed(self):
+        cheapest_flight_within_k_flights = CheapestFlightsWithinKStops()
+        n = 3
+        flights = [[0, 1, 100], [1, 2, 100], [0, 2, 500]]
+        src = 0
+        dst = 2
+        k = 0
+        result = cheapest_flight_within_k_flights.findCheapestPrice(n, flights, src, dst, k)
+        self.assertEqual(result, 500)
+
+    def test_large_k_value(self):
+        cheapest_flight_within_k_flights = CheapestFlightsWithinKStops()
+        n = 4
+        flights = [[0, 1, 100], [1, 2, 100], [2, 3, 100], [0, 3, 500]]
+        src = 0
+        dst = 3
+        k = 2
+        result = cheapest_flight_within_k_flights.findCheapestPrice(n, flights, src, dst, k)
+        self.assertEqual(result, 300)
+
+
+if __name__ == '__main__':
+    unittest.main()