Create minimum-cost-for-tickets.cpp

Author: kamyu104

C++/minimum-cost-for-tickets.cpp

@@ -0,0 +1,23 @@
+// Time:  O(n)
+// space: O(n)
+
+class Solution {
+public:
+    int mincostTickets(vector<int>& days, vector<int>& costs) {
+        static vector<int> durations{1, 7, 30};
+
+        vector<int> dp(days.size() + 1, numeric_limits<int>::max());
+        dp[0] = 0;
+        vector<int> last_buy_days{0, 0, 0};
+        for (int i = 1; i < days.size() + 1; ++i) {
+            for (int j = 0; j < durations.size(); ++j) {
+                while (i - 1 < days.size() &&
+                       days[i-1] > days[last_buy_days[j]]+durations[j] - 1) {
+                    ++last_buy_days[j];  // Time: O(n)
+                }
+                dp[i] = min(dp[i], dp[last_buy_days[j]]+costs[j]);
+            }
+        }
+        return dp.back();
+    }
+};