Leetcode 6. ZigZag Conversion（python）

class Solution(object):
    def convert(self, s, numRows):
        """
        :type s: str
        :type numRows: int
        :rtype: str
        """
        if numRows==1:  return s
    
        res=["" for i in range(len(s))]
        
        i,l=0,-1
        while i<len(s):
            while l<numRows-1 and i<len(s):
                l+=1
                res[l]+=s[i]
                i+=1
            while l>0 and i<len(s):
                l-=1
                res[l]+=s[i]
                i+=1
                
        return ‘‘.join(res)