ZigZag Conversion

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".

class Solution {
public:
     string convert( string s,  int nRows) 
    {
         string* str= new  string[nRows];
         int index= 0;
         while(index<s.length())
        {
             for( int j= 0;j<nRows && index<s.length();j++)
                str[j]+=s[index++];
             for( int j=nRows- 2;j> 0 && index<s.length();j--)
                str[j]+=s[index++];
        }
         string result;
         if(nRows>s.length()) nRows=s.length();
         for( int i= 0;i<nRows;i++)
            result=result+str[i];
         return result;
    }
};