LeetCode-6.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".

思路：

先向下循环numRows次，再对角线循环numRows-2次。调试运行一次就能理解了。

public string Convert(string s, int numRows)
        {
            if (numRows == 1)
                return s;
            string[] res = new string[numRows];
            int i = 0, j, k = numRows - 2,len=s.Length;
            while (i<len)
            {
                for (j = 0; i < len && j < numRows; j++)
                    res[j] += s[i++];
                for (j = k; i < len && j >0; j--)
                    res[j] += s[i++];
            }
            string str = "";
            for (i = 0; i < numRows; i++)
                str += res[i];
            return str;
        }