LeetCode 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".

0				8				16
1			7	9			15	17
2		6		10		14		18
3	5			11	13			19
4				12				20

分两次循环，第一次是列，第二次是斜线。

java需使用stringbuffer才不会超时，使用string超时了。

public class Solution {
    public String convert(String s, int nRows) {
        if (nRows==1) {
            return s;
        }
       
        StringBuffer[]    reBuffers=new StringBuffer[nRows];
        for (int i = 0; i < reBuffers.length; i++) {
            reBuffers[i]=new StringBuffer();
        }
        int i=0,j=0,C=nRows-2;
        while (i<s.length()) {
            for (j = 0; j<nRows&&i<s.length() ;j++) {
        
                reBuffers[j].append(s.charAt(i++));
                
            }
            
            for (j = C; i<s.length()&&j>0;j--) {
                
                reBuffers[j].append(s.charAt(i++));
                
            }
            
        }
        
        StringBuffer    res=new StringBuffer();
        for (int k = 0; k < nRows; k++) {
            res.append(reBuffers[k]);
        }
        return res.toString();
    }
}