6. ZigZag Conversion
难度: 中等
刷题内容
原题连接
- https://leetcode.com/problems/zigzag-conversion/
内容描述
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 s, int numRows);
Example 1:
Input: s = "PAYPALISHIRING", numRows = 3
Output: "PAHNAPLSIIGYIR"
Example 2:
Input: s = "PAYPALISHIRING", numRows = 4
Output: "PINALSIGYAHRPI"
Explanation:
P I N
A L S I G
Y A H R
P I
解题方案
思路 1
参考大神pharrellyhy的思路,
纵向思维考虑，index从0开始，我们要一直自增直到numRows-1，此后又一直自减到0，重复执行。
给个例子容易懂一些：s = “abcdefghijklmn”, numRows = 4
a g m
b f h l n
c e i k
d j
看明白了吗，下来上去，下来上去，zigzag
class Solution(object):
def convert(self, s, numRows):
"""
:type s: str
:type numRows: int
:rtype: str
"""
if numRows == 1 or numRows >= len(s):
return s
res = [''] * numRows
idx, step = 0, 1
for x in s:
res[idx] += x
if idx == 0: ## 第一行，一直向下走
step = 1
elif idx == numRows - 1: ## 最后一行了，向上走
step = -1
idx += step
return ''.join(res)
假设用我上面给的例子，并且在L[index] += x这一行后面打印出index, step, L的值, 输出结果如下：
(0, 1, ['a', '', '', ''])
(1, 1, ['a', 'b', '', ''])
(2, 1, ['a', 'b', 'c', ''])
(3, 1, ['a', 'b', 'c', 'd'])
(2, -1, ['a', 'b', 'ce', 'd'])
(1, -1, ['a', 'bf', 'ce', 'd'])
(0, -1, ['ag', 'bf', 'ce', 'd'])
(1, 1, ['ag', 'bfh', 'ce', 'd'])
(2, 1, ['ag', 'bfh', 'cei', 'd'])
(3, 1, ['ag', 'bfh', 'cei', 'dj'])
(2, -1, ['ag', 'bfh', 'ceik', 'dj'])
(1, -1, ['ag', 'bfhl', 'ceik', 'dj'])
(0, -1, ['agm', 'bfhl', 'ceik', 'dj'])
(1, 1, ['agm', 'bfhln', 'ceik', 'dj'])
