leetcode6

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)

image

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:

image

思路：

1、min(numRows,len(s))用其确定行数有多少

2、用一个ArrayList<StringBuilder>记录每行的数据

3、

image

class Solution {

    public String convert(String s, int numRows) {

        if (numRows == 1) return s;

        List<StringBuilder> rows = new ArrayList<>();

        for (int i = 0; i < Math.min(numRows, s.length()); i++)

            rows.add(new StringBuilder());

        int curRow = 0;

        boolean goingDown = false;

        for (char c : s.toCharArray()) {

            rows.get(curRow).append(c);

            if (curRow == 0 || curRow == numRows - 1) goingDown = !goingDown;

            curRow += goingDown ? 1 : -1;

        }

        StringBuilder ret = new StringBuilder();

        for (StringBuilder row : rows) ret.append(row);

        return ret.toString();

    }

}