ZigZagConversion.cs

// Source : https://leetcode.com/problems/zigzag-conversion/ 
// Author : codeyu 
// Date : 2016/9/28 

/***************************************************************************************
*
* 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". 
*
**********************************************************************************/

using System.Text;
namespace Algorithms
{
    public class Solution006
    {
        public static string Convert(string s, int numRows) 
        {
            if(s.Length <= numRows || numRows <= 1)
            {
                return s;
            }
            StringBuilder result = new StringBuilder();
            var size = 2 * numRows - 2;
            for(var i = 0; i < numRows; i++)
            {
                for(var j = i; j < s.Length; j += size)
                {
                    result.Append(s[j]);
                    if(i > 0 && i < numRows - 1)
                    {
                        var z = j + size - 2 * i;
                        if(z < s.Length)
                        {
                            result.Append(s[z]);
                        }
                        
                    }
                }
            }
            return result.ToString();
        }
    }
}