LeetCode 6. ZigZag Conversion(java)

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：通过观察这个N型的图案的组成，我们发现可以通过从上到下（0 ~ numRows - 1），再从下到上(numRows - 1, 1)，以此为反复，就可以得到想要的排列。所以解决的方法就是创建numRows个StringBuilder，每个StringBuilder都可以储存每行的字母，通过N型的排列来将字母一个个加进对应的行里。

public String convert(String s, int numRows) {
        if (s.length() ==  || numRows <= ) return s;
        int length = s.length(), index = ;
        StringBuilder[] sb = new StringBuilder[numRows];
        for (int i = ; i < numRows; i++) {
            sb[i] = new StringBuilder();
        }
        while (index < length) {
            for (int i = ; i < numRows && index < length; i++) {
                System.out.println(sb[i]);
                sb[i].append(s.charAt(index));
                index++;
            }
            for (int j = numRows - ; j >=  && index < length; j--) {
                sb[j].append(s.charAt(index));
                index++;
            }
        }
        StringBuilder res = new StringBuilder();
        for (int i = ; i < numRows; i++) {
            res.append(sb[i]);
        }
        return res.toString();
    }