Sync LeetCode submission Runtime - 86 ms (72.65%), Memory - 30.7 MB (7.59%)

Author: jimit105

0878-shifting-letters/README.md

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+<p>You are given a string <code>s</code> of lowercase English letters and an integer array <code>shifts</code> of the same length.</p>
+
+<p>Call the <code>shift()</code> of a letter, the next letter in the alphabet, (wrapping around so that <code>&#39;z&#39;</code> becomes <code>&#39;a&#39;</code>).</p>
+
+<ul>
+	<li>For example, <code>shift(&#39;a&#39;) = &#39;b&#39;</code>, <code>shift(&#39;t&#39;) = &#39;u&#39;</code>, and <code>shift(&#39;z&#39;) = &#39;a&#39;</code>.</li>
+</ul>
+
+<p>Now for each <code>shifts[i] = x</code>, we want to shift the first <code>i + 1</code> letters of <code>s</code>, <code>x</code> times.</p>
+
+<p>Return <em>the final string after all such shifts to s are applied</em>.</p>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+
+<pre>
+<strong>Input:</strong> s = &quot;abc&quot;, shifts = [3,5,9]
+<strong>Output:</strong> &quot;rpl&quot;
+<strong>Explanation:</strong> We start with &quot;abc&quot;.
+After shifting the first 1 letters of s by 3, we have &quot;dbc&quot;.
+After shifting the first 2 letters of s by 5, we have &quot;igc&quot;.
+After shifting the first 3 letters of s by 9, we have &quot;rpl&quot;, the answer.
+</pre>
+
+<p><strong class="example">Example 2:</strong></p>
+
+<pre>
+<strong>Input:</strong> s = &quot;aaa&quot;, shifts = [1,2,3]
+<strong>Output:</strong> &quot;gfd&quot;
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>1 &lt;= s.length &lt;= 10<sup>5</sup></code></li>
+	<li><code>s</code> consists of lowercase English letters.</li>
+	<li><code>shifts.length == s.length</code></li>
+	<li><code>0 &lt;= shifts[i] &lt;= 10<sup>9</sup></code></li>
+</ul>

0878-shifting-letters/solution.py

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+# Approach: Cumulative Sum (Prefix Sum)
+
+# Time: O(n)
+# Space: O(n)
+
+from itertools import accumulate
+
+class Solution:
+    def shiftingLetters(self, s: str, shifts: List[int]) -> str:
+        s = list(s)
+
+        # Use accumulate to get cumulative shifts from right to left
+    # We reverse the shifts array first, then reverse the result
+        cum_shifts = list(accumulate(shifts[::-1]))[::-1]
+
+        for i in range(len(s)):
+            new_char = chr((ord(s[i]) - ord('a') + cum_shifts[i]) % 26 + ord('a'))
+            s[i] = new_char
+
+        return ''.join(s)
+