LeetCode 字符串转换Z形状(6. ZigZag Conversion)

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 s, int numRows);

Example 1:Input: s = “PAYPALISHIRING”, numRows = 3

Output: “PAHNAPLSIIGYIR”

Example 2:Input: s = “PAYPALISHIRING”, numRows = 4

Output: “PINALSIGYAHRPI”

Explanation:

P I N
A L S I G
Y A H R
P I

public String Convert(String s, int numRows)
            {

                if (numRows == 1) return s;

                StringBuilder ret = new StringBuilder();
                int n = s.Length;
                int cycleLen = 2 * numRows - 2;

                for (int i = 0; i < numRows; i++)
                {
                    for (int j = 0; j + i < n; j += cycleLen)
                    {
                        ret.Append(s[j + i]);
                        if (i != 0 && i != numRows - 1 && j + cycleLen - i < n)
                            ret.Append(s[j + cycleLen - i]);
                    }
                }
                return ret.ToString();
            }