cheapest flight problem

Author: Alagappan Maruthappan

cheapest_flight.py

@@ -0,0 +1,43 @@
+# https://leetcode.com/problems/cheapest-flights-within-k-stops/submissions/
+
+import sys
+
+
+class Solution:
+    def findCheapestPrice(self, n, flights, src, dst, K):
+        """
+        :type n: int
+        :type flights: List[List[int]]
+        :type src: int
+        :type dst: int
+        :type K: int
+        :rtype: int
+        """
+        cities = [[] for _ in range(n)]
+        for s, d, c in flights:
+            cities[s].append((d, c))
+
+        distances_from_src = [sys.maxsize for _ in range(n)]
+        distances_from_src[src] = 0
+        for stop in range(K + 1):
+            new_distances_from_src = distances_from_src[:]
+            change = False
+            for city in range(n):
+                for a_city, a_city_cost in cities[city]:
+                    new_cost = a_city_cost + distances_from_src[city]
+                    if new_cost < new_distances_from_src[a_city]:
+                        new_distances_from_src[a_city] = new_cost
+                        change = True
+            distances_from_src = new_distances_from_src
+            if not change:
+                break
+
+        cost = distances_from_src[dst]
+        return cost if cost != sys.maxsize else -1
+
+
+assert Solution().findCheapestPrice(
+    3, [[0, 1, 100], [1, 2, 100], [0, 2, 500]], 0, 2, 1) == 200
+
+assert Solution().findCheapestPrice(
+    3, [[0, 1, 100], [1, 2, 100], [0, 2, 500]], 0, 2, 0) == 500