Z字形变换

def convert(s: str, numRows: int) -> str:
    strList = []
    length = len(s)
    if numRows > 2:
        interNum = numRows - 2
        for i in range(0, length, numRows + interNum):
            strList.append(s[i])
        for n in range(1, numRows - 1):
            for i in range(n, length, numRows + interNum):
                strList.append(s[i])
                if i + numRows + interNum - 2 * n < length:
                    strList.append(s[i + numRows + interNum - 2 * n])
        for i in range(numRows - 1, length, numRows + interNum):
            strList.append(s[i])
    else:
        for n in range(numRows):
            for i in range(n, length, numRows):
                strList.append(s[i])
    return ''.join(strList)