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".

Difficulty: Easy

 

最直接的遍历：272ms

public string Convert(string s, int numRows) {
           if (numRows < 2||s.Length<3||s.Length<=numRows) return s;

            List<char> list=new List<char>();
            int temp = 2*numRows - 2;
            for (int j = 1; j <= numRows; j++)
            {
                for (int i = 1; i <= s.Length; i++)
                {
                    int y = i%temp;
                    if (y == j || numRows - (y - numRows) == j || (y==0&&j==2)) list.Add(s[i - 1]);
                }
            }
           
            return new string(list.ToArray());
    }

很直接的遍历：188ms

public string Convert(string s, int numRows) {
           int len = s.Length;
            if (numRows < 2||s.Length<3||len<=numRows) return s;
            
            StringBuilder[] sb=new StringBuilder[numRows];
            for (int i = 0; i < sb.Length; i++)
            {
                sb[i]=new StringBuilder();
            }

            int j = 0;
            while (j < len)
            {
                for (int n = 0; n < numRows && j < len; n++)
                {
                    sb[n].Append(s[j++]);
                }
                for (int n = numRows - 2; n >= 1 && j < len; n--)
                {
                    sb[n].Append(s[j++]);
                }
            }

            for (int i = 1; i < sb.Length; i++)
            {
                sb[0].Append(sb[i]);
            }
            return sb[0].ToString();
    }