【leetcode】ZigZag Conversion

题目简述

The string "PAYPALISHIRING" is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility)

P A H N
A P L S I I G
Y I R
And then read line by line: "PAHNAPLSIIGYIR"
Write the code that will take a string and make this conversion given a number of rows:

string convert(string text, int nRows);
convert("PAYPALISHIRING", 3) should return "PAHNAPLSIIGYIR".

解题思路：

这个题目有两种做法：第一种是模拟，也就是说我们可以有几行就开几个数组都存起来，最后合到一起就可以了；另一种方法是找规律。因为第一种比较直观，故代码实现了第一种思路：

class Solution:
    # @return a string
    def convert(self, s, nRows):
        if nRows == 1:
            return s
        gap = nRows - 2
        res = []
        for i in range(nRows):
            res.append([])
        i = 0
        while i < len(s):
            for j in range(nRows):
                if i >= len(s):
                    break
                res[j] += s[i]
                i += 1
            for j in range(gap,0,-1):
                if i >= len(s):
                    break
                res[j] += s[i]
                i += 1
        ress = ""
        for i in res:
            for j in i:
                ress += j
        return ress