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Author: NamVr

1025-minimum-cost-for-tickets/README.md

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+<p>You have planned some train traveling one year in advance. The days of the year in which you will travel are given as an integer array <code>days</code>. Each day is an integer from <code>1</code> to <code>365</code>.</p>
+
+<p>Train tickets are sold in <strong>three different ways</strong>:</p>
+
+<ul>
+	<li>a <strong>1-day</strong> pass is sold for <code>costs[0]</code> dollars,</li>
+	<li>a <strong>7-day</strong> pass is sold for <code>costs[1]</code> dollars, and</li>
+	<li>a <strong>30-day</strong> pass is sold for <code>costs[2]</code> dollars.</li>
+</ul>
+
+<p>The passes allow that many days of consecutive travel.</p>
+
+<ul>
+	<li>For example, if we get a <strong>7-day</strong> pass on day <code>2</code>, then we can travel for <code>7</code> days: <code>2</code>, <code>3</code>, <code>4</code>, <code>5</code>, <code>6</code>, <code>7</code>, and <code>8</code>.</li>
+</ul>
+
+<p>Return <em>the minimum number of dollars you need to travel every day in the given list of days</em>.</p>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+
+<pre>
+<strong>Input:</strong> days = [1,4,6,7,8,20], costs = [2,7,15]
+<strong>Output:</strong> 11
+<strong>Explanation:</strong> For example, here is one way to buy passes that lets you travel your travel plan:
+On day 1, you bought a 1-day pass for costs[0] = $2, which covered day 1.
+On day 3, you bought a 7-day pass for costs[1] = $7, which covered days 3, 4, ..., 9.
+On day 20, you bought a 1-day pass for costs[0] = $2, which covered day 20.
+In total, you spent $11 and covered all the days of your travel.
+</pre>
+
+<p><strong class="example">Example 2:</strong></p>
+
+<pre>
+<strong>Input:</strong> days = [1,2,3,4,5,6,7,8,9,10,30,31], costs = [2,7,15]
+<strong>Output:</strong> 17
+<strong>Explanation:</strong> For example, here is one way to buy passes that lets you travel your travel plan:
+On day 1, you bought a 30-day pass for costs[2] = $15 which covered days 1, 2, ..., 30.
+On day 31, you bought a 1-day pass for costs[0] = $2 which covered day 31.
+In total, you spent $17 and covered all the days of your travel.
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>1 &lt;= days.length &lt;= 365</code></li>
+	<li><code>1 &lt;= days[i] &lt;= 365</code></li>
+	<li><code>days</code> is in strictly increasing order.</li>
+	<li><code>costs.length == 3</code></li>
+	<li><code>1 &lt;= costs[i] &lt;= 1000</code></li>
+</ul>

1025-minimum-cost-for-tickets/solution.cpp

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+class Solution {
+public:
+    int mincostTickets(vector<int>& days, vector<int>& costs) {
+        int lastDay = days[days.size() - 1];
+        vector<int> dp(lastDay + 1, 0);
+        
+        int i = 0;
+        for (int day = 1; day <= lastDay; day++) {
+            if (day < days[i]) {
+                dp[day] = dp[day - 1];
+            } else {
+                i++;
+                dp[day] = min({dp[day - 1] + costs[0],
+                               dp[max(0, day - 7)] + costs[1],
+                               dp[max(0, day - 30)] + costs[2]});
+            }
+        }
+     
+        return dp[lastDay];
+    }
+};