字符串操作 —— 6_Z字形变换

1. 6_Z字形变换

/*
输入: s = "LEETCODEISHIRING", numRows = 4
输出: "LDREOEIIECIHNTSG"
解释:
L     D     R
E   O E   I I
E C   I H   N
T     S     G
*/
class Solution {
    public String convert(String s, int numRows) {
        if(s == null || s.length() == 0 || numRows <= 1) return s;
        StringBuilder[] array = new StringBuilder[numRows];
        for(int i=0; i < numRows; i++) array[i] = new StringBuilder();
        int dir = 1;
        int index = 0;
        for(char c : s.toCharArray()){
            array[index].append(c);
            index += dir;
            if(index == 0 || index == numRows-1) dir = -dir;
        }
        StringBuilder ret = new StringBuilder();
        for(int i=0; i < numRows; i++) ret.append(array[i]);
        return ret.toString();
    }
}

class Solution {
    public String convert(String s, int numRows) {

        if (numRows == 1) return s;

        StringBuilder ret = new StringBuilder();
        int n = s.length();
        int cycleLen = 2 * numRows - 2;

        for (int i = 0; i < numRows; i++) {
            for (int j = 0; j + i < n; j += cycleLen) {
                ret.append(s.charAt(j + i));
                if (i != 0 && i != numRows - 1 && j + cycleLen - i < n)
                    ret.append(s.charAt(j + cycleLen - i));
            }
        }
        return ret.toString();
    }
}