6、ZigZag Conversion

题目：

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：

要理解题目说的意思，虽然对于没有相关背景的人可能会理解错误。下面一图便能解释清楚。

0				8				16
1			7	9			15	17
2		6		10		14		18
3	5			11	13			19
4				12				20

c++版本：

class Solution {
public:
string convert(string s, int numRows) {
int index=0,row=0,add_v=1;
string ans = "";
string res[numRows];
if(numRows==1)return s;
while(index<s.size())
{
res[row] += s[index];
if(row==0)
add_v=1;
if(row==numRows-1)
add_v = -1;
index++;
row += add_v;
}
for(int i=0;i<numRows;i++)
ans += res[i];
return ans;
}

};

python版本：

class Solution(object):
def convert(self, s, numRows):
"""
:type s: str
:type numRows: int
:rtype: str
"""
index,row,add_v = 0,0,1
res = []
ans = ""
for i in range(numRows):
res.append([])
if(numRows==1):return s
while index<len(s):
res[row].append(s[index])
if(row==0):
add_v = 1
elif(row==numRows-1):
add_v = -1
row += add_v
index += 1
for l in res:
for c in l:
ans += c
return ans