ZigZag Conversion

class Solution:
    def convert(self, s: str, numRows: int) -> str:
        if numRows==1:return s
        
        res=""
        for r in range(numRows):
            increment=2*(numRows-1)
            for i in range(r,len(s),increment):
                res+=s[i]
                if(r>0 and r<numRows-1 and i + increment-2*r<len(s)):
                    res+=s[i+increment-2*r]
                    
        return res