6. Zigzag Conversion

• categories: Code, Interview Question, leetcode, Medium
• source: https://leetcode.com/problems/zigzag-conversion
• topics: String Manipulation

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”

Idea

Traverse the sttring using two inner loops

class Solution:
    def convert(self, s: str, numRows: int) -> str:
        rows = ["" for _ in range(numRows)]
        i = 0
        while i < len(s):
            for j in range(numRows):
                if i < len(s):
                    rows[j] += s[i]
                    j += 1
                    i += 1
                else:
                    break
            for j in reversed(range(1, numRows-1)):
                if i < len(s):
                    rows[j] += s[i]
                    j += 1
                    i += 1
                else:
                    break
        return "".join(rows)