6 ZigZag Conversion

Method: Store the information according to their layer. Use extra value to store the direction and the current layer value.

注意： 如果numRows == 1 没有必要进行conversion 这个情况单独列出来一下

class Solution(object):
    def convert(self, s, numRows):
        """
        :type s: str
        :type numRows: int
        :rtype: str
        """
        if numRows == 1:
            return s
        d = [ "" for i in range(numRows)]
        current_row = 0
        current_direction = -1
        for i in s:
            print current_row
            d[current_row] += i
            if current_row == 0 or current_row == numRows - 1:
                current_direction *= (-1)
            current_row += current_direction
        ans = ""
        for i in d:
            ans += i
        return ans