From f7d48aaeac388548bafc011a2960d34ebbd6b70e Mon Sep 17 00:00:00 2001
From: deepshekhardas <deepshekharadas1234@gmail.com>
Date: Sat, 11 Jul 2026 16:16:21 +0530
Subject: [PATCH 1/3] feat: add zigzag conversion algorithm

---
 strings/zigzag_conversion.py | 49 ++++++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)
 create mode 100644 strings/zigzag_conversion.py

diff --git a/strings/zigzag_conversion.py b/strings/zigzag_conversion.py
new file mode 100644
index 000000000000..adc1c5ffeb14
--- /dev/null
+++ b/strings/zigzag_conversion.py
@@ -0,0 +1,49 @@
+from __future__ import annotations
+
+
+def zigzag_convert(s: str, num_rows: int) -> str:
+    """
+    Convert a string to zigzag pattern and read it row by row.
+
+    The string is written in a zigzag pattern on num_rows rows:
+    - Characters at index 0, num_rows, 2*num_rows, ... go to row 0
+    - Characters at index 1, num_rows+1, 2*num_rows+1, ... go to row 1
+    - And so on until row num_rows-1
+    - Then the direction reverses (going up)
+
+    Args:
+        s: The input string to convert
+        num_rows: Number of rows in the zigzag pattern
+
+    Returns:
+        The string read row by row from top to bottom
+
+    >>> zigzag_convert("PAYPALISHIRING", 3)
+    'PAHNAPLSIIGYIR'
+    >>> zigzag_convert("PAYPALISHIRING", 4)
+    'PINALSIGYAHRPI'
+    >>> zigzag_convert("A", 1)
+    'A'
+    >>> zigzag_convert("AB", 1)
+    'BA'
+    """
+    if num_rows == 1 or num_rows >= len(s):
+        return s
+
+    rows: list[list[str]] = [[] for _ in range(num_rows)]
+    current_row = 0
+    going_down = False
+
+    for char in s:
+        rows[current_row].append(char)
+        if current_row == 0 or current_row == num_rows - 1:
+            going_down = not going_down
+        current_row += 1 if going_down else -1
+
+    return "".join("".join(row) for row in rows)
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()
\ No newline at end of file

From 2061cd60f35c4bffd5241026cb17383394f66fef Mon Sep 17 00:00:00 2001
From: deepshekhardas <deepshekharadas1234@gmail.com>
Date: Sat, 11 Jul 2026 18:21:39 +0530
Subject: [PATCH 2/3] fix: replace conditional expression with explicit if/else
 for ruff compatibility

---
 strings/zigzag_conversion.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/strings/zigzag_conversion.py b/strings/zigzag_conversion.py
index adc1c5ffeb14..f9291b99137d 100644
--- a/strings/zigzag_conversion.py
+++ b/strings/zigzag_conversion.py
@@ -38,7 +38,10 @@ def zigzag_convert(s: str, num_rows: int) -> str:
         rows[current_row].append(char)
         if current_row == 0 or current_row == num_rows - 1:
             going_down = not going_down
-        current_row += 1 if going_down else -1
+        if going_down:
+            current_row += 1
+        else:
+            current_row -= 1
 
     return "".join("".join(row) for row in rows)
 

From ffdd00493b521fc2476f6955ec95f70dbba4c9d5 Mon Sep 17 00:00:00 2001
From: "pre-commit-ci[bot]"
 <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Date: Mon, 20 Jul 2026 05:53:25 +0000
Subject: [PATCH 3/3] [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci
---
 strings/zigzag_conversion.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/strings/zigzag_conversion.py b/strings/zigzag_conversion.py
index f9291b99137d..471c51a7cc3a 100644
--- a/strings/zigzag_conversion.py
+++ b/strings/zigzag_conversion.py
@@ -49,4 +49,4 @@ def zigzag_convert(s: str, num_rows: int) -> str:
 if __name__ == "__main__":
     import doctest
 
-    doctest.testmod()
\ No newline at end of file
+    doctest.testmod()