6.-zigzag-conversion.md

6. 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);
  

Analysis

We can keep an counter to record where this character should be(in which of the lines). Then we add that into a list to record it and link the list up.

class Solution:
    def convert(self, s: str, numRows: int) -> str:
        ans=[""]*numRows
        if numRows==1:
            return s
        n=len(s)
        index=0
        step=1
        for i in range(n):
            ans[index]+=s[i]
            if index==numRows-1:
                step=-1
            if index==0:
                step=1
            index+=step
        answer=""
        for i in ans:
            answer+=i
        return answer