solves minimum cost for tickets (#983) in python

python/minimum_cost_for_tickets.py

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+# https://leetcode.com/problems/minimum-cost-for-tickets/description/
+# T: O(N) where N is the last day of travel
+# S: O(N) where N is the last day of travel
+
+class Solution:
+    def mincostTickets(self, days, costs):
+        # Create a list of size days[-1] + 1 and initialize it with 0's
+        dp = [0] * (days[-1] + 1)
+
+        # Create a set of travel days
+        travel_days = set(days)
+
+        # Iterate over the range of 1 to len(dp) with a step of 1
+        for i in range(1, len(dp)):
+            # If the current day is not in the set of travel days
+            if i not in travel_days:
+                # Set its cost to the cost of traveling on the previous day
+                dp[i] = dp[i - 1]
+            else:
+                # Calculate the minimum cost for traveling on that day
+                dp[i] = min(dp[max(0, i - 1)] + costs[0],
+                            dp[max(0, i - 7)] + costs[1],
+                            dp[max(0, i - 30)] + costs[2])
+
+        # Return the last element of this list which will be the minimum cost of travel for all days
+        return dp[-1]