```
class Solution(object):
def convert(self, s, numRows):
"""
:type s: str
:type numRows: int
:rtype: str
"""
lens = len(s)
if lens <= numRows or numRows <= 1:
return s
else:
strre = ""
lenstr = (numRows - 1) * 2
i = j = k = m = 0
lenstrre = 0
while lenstrre < lens:
strre = strre + s[j]
lenstrre += 1
if not j % (lenstr / 2):
j += lenstr
else:
m += 1
k = lenstr - j if m == 1 else lenstr + k
if k >= lens:
i += 1
j = i
m = 0
else:
strre = strre + s[k]
lenstrre += 1
j += lenstr
if j >= lens:
i += 1
j = i
m = 0
return strre
```