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".

分析

这道题就是要根据z字形遍历，我们模拟一遍过程可以发现遍历的规律，可以用循环解决，先遍历下去，又向上。然后重复这个步骤，向下，向上！

代码

public String convert(String s, int nRows) {
        char[] c = s.toCharArray();
        int len = c.length;
        StringBuilder[] sb = new StringBuilder[nRows];
        for(int i=0;i<sb.length;i++)
            sb[i] = new StringBuilder();
        int i=0;
        while(i<len) {
            for(int index=0;index<nRows && i<len;index++) {
                sb[index].append(c[i]);
                i++;
            }
            for(int index=nRows-2;index>=1 && i<len;index--) {
                sb[index].append(c[i]);
                i++;
            }
        }
        for(int index=1;index<sb.length;index++) {
            sb[0].append(sb[index]);
        }
        return sb[0].toString();
    }

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