README.md

6. ZigZag Conversion

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

Solutions (Python)

1. Solution

class Solution:
    def convert(self, s: str, numRows: int) -> str:
        rows = [[] for _ in range(numRows)]
        i = 0
        increase = True

        for ch in s:
            rows[i].append(ch)

            i += 1 if increase else -1
            if i == numRows:
                i -= 2
                increase = False
            if i <= 0:
                increase = True

        return ''.join(''.join(r) for r in rows)