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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

class Solution: def convert(self, s: str, numRows: int) -> str: if len(s) <= 1 or numRows == 1: return s res = [''] * numRows periodic = 2 * numRows - 2 for i in range(len(s)): index = i % periodic if index <= numRows - 1: res[index] += s[i] else: index = periodic - index res[index] += s[i] return ''.join(res)

The main gist of this question is to get the idea of how we can use StringBuilder to append the characters at a particular level of the row. It is being explained in a detailed way in the video. 
Time Complexity: O(n)  // for traversing through each character of the string.

Space Complexity: O(n)  // for storing the result in StringBuilder.