From 1464db0d1ac1cccecda5109b8a7956757c95b72e Mon Sep 17 00:00:00 2001
From: Siddhartha Dutta <siddharthadutta@protonmail.com>
Date: Sun, 5 Jan 2025 00:25:07 +0000
Subject: [PATCH] Jan 5

---
 .../README.md                                 |  4 +-
 .../Shifting Letters II.py                    | 38 +++++++++++++++++++
 2 files changed, 40 insertions(+), 2 deletions(-)
 create mode 100644 2025-01-January-LeetCoding-Challenge/Shifting Letters II.py

diff --git a/2025-01-January-LeetCoding-Challenge/README.md b/2025-01-January-LeetCoding-Challenge/README.md
index dad602d..80f98ea 100644
--- a/2025-01-January-LeetCoding-Challenge/README.md
+++ b/2025-01-January-LeetCoding-Challenge/README.md
@@ -7,7 +7,7 @@
 | January 2  | [2559. Count Vowel Strings in Ranges](https://leetcode.com/problems/count-vowel-strings-in-ranges/) | Medium | Solved |
 | January 3  | [2270. Number of Ways to Split Array](https://leetcode.com/problems/number-of-ways-to-split-array/) | Medium | Solved |
 | January 4  | [1930. Unique Length-3 Palindromic Subsequences](https://leetcode.com/problems/unique-length-3-palindromic-subsequences/) | Medium | Solved |
-| January 5  | []() |  |  |
+| January 5  | [2381. Shifting Letters II](https://leetcode.com/problems/shifting-letters-ii/) | Medium | Solved |
 | January 6  | []() |  |  |
 | January 7  | []() |  |  |
 | January 8  | []() |  |  |
@@ -40,5 +40,5 @@
 | Level  | Problems | Solved | Unsolved |
 | ---    | --- | --- | --- |
 | Easy   | 1 | 1 | 0 |
-| Medium | 3 | 3 | 0 |
+| Medium | 4 | 4 | 0 |
 | Hard   | 0 | 0 | 0 |
diff --git a/2025-01-January-LeetCoding-Challenge/Shifting Letters II.py b/2025-01-January-LeetCoding-Challenge/Shifting Letters II.py
new file mode 100644
index 0000000..0fb47a4
--- /dev/null
+++ b/2025-01-January-LeetCoding-Challenge/Shifting Letters II.py	
@@ -0,0 +1,38 @@
+from itertools import accumulate
+from typing import List
+
+
+class Solution:
+    def shiftingLetters(self, s: str, shifts: List[List[int]]) -> str:
+        # line sweep algorithm
+        line = [0] * (len(s) + 1)  # account for shift after last element
+        for start, end, direction in shifts:
+            if direction == 1:
+                # start shifting from start
+                line[start] += 1
+                # stop shifting after end
+                line[end + 1] -= 1
+            else:
+                line[start] -= 1
+                line[end + 1] += 1
+        # prefix sum to calculate total shifts
+        line = accumulate(line)
+
+        result = ''
+        for ch, sh in zip(s, line):
+            result += chr(ord('a') + ((ord(ch) - ord('a') + sh) % 26))
+        return result
+
+
+def main():
+    s = 'abc'
+    shifts = [[0, 1, 0], [1, 2, 1], [0, 2, 1]]
+    assert Solution().shiftingLetters(s, shifts) == 'ace'
+
+    s = 'dztz'
+    shifts = [[0, 0, 0], [1, 1, 1]]
+    assert Solution().shiftingLetters(s, shifts) == 'catz'
+
+
+if __name__ == '__main__':
+    main()