LeetCode 6: ZigZag Conversion

Difficulty: 3

Frequency: 1

Problem:

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"

.

Solution:

class Solution {
public:
string convert(string s, int nRows) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
if (nRows<=1) //Without this condition will cause Memory Limit Exceeded.
return s;

string answer;

if (s.size()==0)
return answer;

int k, index;
for (int i = 0; i<nRows; i++)
{
for (k = 0, index = i; index<s.size(); k++, index = (2*nRows - 2)*k+i)
{
answer += s[index];

if (i==0||i==nRows-1)
continue;

if ((index += 2*(nRows-i-1))<s.size())
{
answer += s[index];
}
}
}
return answer;
}
};

Notes:

If without condition judgement nRows<=1, Memory Limits Exceeded will occur.nRows<=1