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6. Zigzag Conversion

String

Problem - Zigzag Conversion

Medium

The string "PAYPALISHIRING" is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility)

P   A   H   N
A P L S I I G
Y   I   R

And then read line by line: "PAHNAPLSIIGYIR"

Write the code that will take a string and make this conversion given a number of rows:

string convert(string s, int numRows);

 

Example 1:

Input: s = "PAYPALISHIRING", numRows = 3
Output: "PAHNAPLSIIGYIR"

Example 2:

Input: s = "PAYPALISHIRING", numRows = 4
Output: "PINALSIGYAHRPI"
Explanation:
P     I    N
A   L S  I G
Y A   H R
P     I

Example 3:

Input: s = "A", numRows = 1
Output: "A"

 

Constraints:

  • 1 <= s.length <= 1000
  • s consists of English letters (lower-case and upper-case), ',' and '.'.
  • 1 <= numRows <= 1000

Solutions

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class Solution:
    def convert(self, s: str, numRows: int) -> str:

        if numRows == 1 or len(s) <= numRows:
            return s

        rows = [''] * numRows
        current_row = 0
        going_down = False

        for ch in s:
            rows[current_row] += ch
            if current_row == 0 or current_row == numRows - 1:
                going_down = not going_down
            if going_down:
                current_row += 1
            else:
                current_row -= 1
        result = ''.join(rows)
        return result

Submission Stats:

  • Runtime: 7 ms (88.03%)
  • Memory: 18 MB (29.20%)