Sync LeetCode submission Runtime - 71 ms (56.08%), Memory - 18.9 MB (63.13%)

Author: jimit105

0227-basic-calculator-ii/README.md

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+<p>Given a string <code>s</code> which represents an expression, <em>evaluate this expression and return its value</em>.&nbsp;</p>
+
+<p>The integer division should truncate toward zero.</p>
+
+<p>You may assume that the given expression is always valid. All intermediate results will be in the range of <code>[-2<sup>31</sup>, 2<sup>31</sup> - 1]</code>.</p>
+
+<p><strong>Note:</strong> You are not allowed to use any built-in function which evaluates strings as mathematical expressions, such as <code>eval()</code>.</p>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+<pre><strong>Input:</strong> s = "3+2*2"
+<strong>Output:</strong> 7
+</pre><p><strong class="example">Example 2:</strong></p>
+<pre><strong>Input:</strong> s = " 3/2 "
+<strong>Output:</strong> 1
+</pre><p><strong class="example">Example 3:</strong></p>
+<pre><strong>Input:</strong> s = " 3+5 / 2 "
+<strong>Output:</strong> 5
+</pre>
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>1 &lt;= s.length &lt;= 3 * 10<sup>5</sup></code></li>
+	<li><code>s</code> consists of integers and operators <code>(&#39;+&#39;, &#39;-&#39;, &#39;*&#39;, &#39;/&#39;)</code> separated by some number of spaces.</li>
+	<li><code>s</code> represents <strong>a valid expression</strong>.</li>
+	<li>All the integers in the expression are non-negative integers in the range <code>[0, 2<sup>31</sup> - 1]</code>.</li>
+	<li>The answer is <strong>guaranteed</strong> to fit in a <strong>32-bit integer</strong>.</li>
+</ul>

0227-basic-calculator-ii/solution.py

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+# Time: O(n)
+# Space: O(1)
+
+class Solution:
+    def calculate(self, s: str) -> int:
+        if not s:
+            return 0
+
+        length = len(s)
+        current_number = 0
+        last_number = 0
+        result = 0
+        operation = '+'
+
+        for i in range(length):
+            current_char = s[i]
+
+            if current_char.isdigit():
+                current_number = (current_number * 10) + int(current_char)
+
+            if (not current_char.isdigit() and not current_char.isspace()) or i == length - 1:
+                if operation in ['+', '-']:
+                    result += last_number
+                    last_number = current_number if operation == '+' else -current_number
+                elif operation == '*':
+                    last_number = last_number * current_number
+                elif operation == '/':
+                    last_number = int(last_number / current_number)
+
+                operation = current_char
+                current_number = 0
+        
+        result += last_number
+        return result