[LeetCode Sync] Runtime - 3 ms (75.28%), Memory - 21.9 MB (77.76%)

Author: NinePiece2

Solutions/0890-lemonade-change/README.md

@@ -0,0 +1,38 @@
+<p>At a lemonade stand, each lemonade costs <code>$5</code>. Customers are standing in a queue to buy from you and order one at a time (in the order specified by bills). Each customer will only buy one lemonade and pay with either a <code>$5</code>, <code>$10</code>, or <code>$20</code> bill. You must provide the correct change to each customer so that the net transaction is that the customer pays <code>$5</code>.</p>
+
+<p>Note that you do not have any change in hand at first.</p>
+
+<p>Given an integer array <code>bills</code> where <code>bills[i]</code> is the bill the <code>i<sup>th</sup></code> customer pays, return <code>true</code> <em>if you can provide every customer with the correct change, or</em> <code>false</code> <em>otherwise</em>.</p>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+
+<pre>
+<strong>Input:</strong> bills = [5,5,5,10,20]
+<strong>Output:</strong> true
+<strong>Explanation:</strong> 
+From the first 3 customers, we collect three $5 bills in order.
+From the fourth customer, we collect a $10 bill and give back a $5.
+From the fifth customer, we give a $10 bill and a $5 bill.
+Since all customers got correct change, we output true.
+</pre>
+
+<p><strong class="example">Example 2:</strong></p>
+
+<pre>
+<strong>Input:</strong> bills = [5,5,10,10,20]
+<strong>Output:</strong> false
+<strong>Explanation:</strong> 
+From the first two customers in order, we collect two $5 bills.
+For the next two customers in order, we collect a $10 bill and give back a $5 bill.
+For the last customer, we can not give the change of $15 back because we only have two $10 bills.
+Since not every customer received the correct change, the answer is false.
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>1 &lt;= bills.length &lt;= 10<sup>5</sup></code></li>
+	<li><code>bills[i]</code> is either <code>5</code>, <code>10</code>, or <code>20</code>.</li>
+</ul>

Solutions/0890-lemonade-change/solution.py

@@ -0,0 +1,18 @@
+class Solution:
+    def lemonadeChange(self, bills: List[int]) -> bool:
+        fives = tens = 0
+        for bill in bills:
+            if bill == 5:
+                fives += 1
+            elif bill == 10:
+                tens += 1
+                fives -= 1
+            else: #20
+                if tens:
+                    tens -= 1
+                    fives -= 1
+                else:
+                    fives -= 3
+            if fives < 0:
+                return False
+        return True