Sync LeetCode submission Runtime - 67 ms (45.05%), Memory - 41.2 MB (49.85%)

Author: jimit105

2465-shifting-letters-ii/README.md

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+<p>You are given a string <code>s</code> of lowercase English letters and a 2D integer array <code>shifts</code> where <code>shifts[i] = [start<sub>i</sub>, end<sub>i</sub>, direction<sub>i</sub>]</code>. For every <code>i</code>, <strong>shift</strong> the characters in <code>s</code> from the index <code>start<sub>i</sub></code> to the index <code>end<sub>i</sub></code> (<strong>inclusive</strong>) forward if <code>direction<sub>i</sub> = 1</code>, or shift the characters backward if <code>direction<sub>i</sub> = 0</code>.</p>
+
+<p>Shifting a character <strong>forward</strong> means replacing it with the <strong>next</strong> letter in the alphabet (wrapping around so that <code>&#39;z&#39;</code> becomes <code>&#39;a&#39;</code>). Similarly, shifting a character <strong>backward</strong> means replacing it with the <strong>previous</strong> letter in the alphabet (wrapping around so that <code>&#39;a&#39;</code> becomes <code>&#39;z&#39;</code>).</p>
+
+<p>Return <em>the final string after all such shifts to </em><code>s</code><em> are applied</em>.</p>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+
+<pre>
+<strong>Input:</strong> s = &quot;abc&quot;, shifts = [[0,1,0],[1,2,1],[0,2,1]]
+<strong>Output:</strong> &quot;ace&quot;
+<strong>Explanation:</strong> Firstly, shift the characters from index 0 to index 1 backward. Now s = &quot;zac&quot;.
+Secondly, shift the characters from index 1 to index 2 forward. Now s = &quot;zbd&quot;.
+Finally, shift the characters from index 0 to index 2 forward. Now s = &quot;ace&quot;.</pre>
+
+<p><strong class="example">Example 2:</strong></p>
+
+<pre>
+<strong>Input:</strong> s = &quot;dztz&quot;, shifts = [[0,0,0],[1,1,1]]
+<strong>Output:</strong> &quot;catz&quot;
+<strong>Explanation:</strong> Firstly, shift the characters from index 0 to index 0 backward. Now s = &quot;cztz&quot;.
+Finally, shift the characters from index 1 to index 1 forward. Now s = &quot;catz&quot;.
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>1 &lt;= s.length, shifts.length &lt;= 5 * 10<sup>4</sup></code></li>
+	<li><code>shifts[i].length == 3</code></li>
+	<li><code>0 &lt;= start<sub>i</sub> &lt;= end<sub>i</sub> &lt; s.length</code></li>
+	<li><code>0 &lt;= direction<sub>i</sub> &lt;= 1</code></li>
+	<li><code>s</code> consists of lowercase English letters.</li>
+</ul>

2465-shifting-letters-ii/solution.py

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+# Approach: Cumulative Shift
+
+# n = length of shifts array, m = length of string
+# Time: O(n + m)
+# Space: O(m)
+
+class Solution:
+    def shiftingLetters(self, s: str, shifts: List[List[int]]) -> str:
+        n = len(s)
+        # Create array to track cumulative shifts for each position
+        shift_count = [0] * n
+
+        for start, end, direction in shifts:
+            # Add 1 for forward shift, -1 for backward shift
+            delta = 1 if direction == 1 else -1
+            shift_count[start] += delta
+
+            if end + 1 < n: # Cancel out effect after end position
+                shift_count[end + 1] -= delta
+
+        # Calculate prefix sum to get total shifts for each position
+        for i in range(1, n):
+            shift_count[i] += shift_count[i - 1]
+        
+        # Apply shifts all at once using modulo arithmetic
+        result = []
+        for i in range(n):
+            # Calculate new character position
+            new_pos = (ord(s[i]) - ord('a') + shift_count[i]) % 26
+            result.append(chr(ord('a') + new_pos))
+
+        return ''.join(result)
+