leetcode6. Z 字形变换

6. Z 字形变换

法一：一开始自己写的史山代码.

 

class Solution {
    public String convert(String s, int numRows) {
        if(numRows == 1)  return s;
        ArrayList<char[]> zConvert = new ArrayList<>();
        int sLen = s.length();
        for(int i = 0;i < sLen;i += (2 * numRows - 2)){
            char[] rows = new char[numRows];
            for(int j = 0;j < numRows;++j)  rows[j] = ' ';
            for(int j = 0;j < numRows && (i + j) < sLen;++j)  rows[j] = s.charAt(i + j);
            zConvert.add(rows);
            for(int j = i + numRows;(j - i) < 2 * (numRows - 1) && j < sLen;++j){
                char[] diagonal = new char[numRows];
                for(int k = 0;k < numRows;++k)  diagonal[k] = ' ';
                diagonal[2 * (numRows - 1) - (j - i)] = s.charAt(j);
                zConvert.add(diagonal);
            }
        }
        int zConvertLen = zConvert.size();
        char[] resChar = new char[sLen];
        for(int i = 0,t = 0;t < sLen && i < numRows;++i){
            for(int j = 0;t < sLen && j < zConvertLen;++j){
                if(zConvert.get(j)[i] != ' ')  resChar[t++] = zConvert.get(j)[i];
            }
        }
        return new String(resChar);
    }
}

 

法二：

 

class Solution {
    public String convert(String s, int numRows) {
        if(numRows == 1 || numRows >= s.length()) return s;
        List<StringBuilder> rows = new ArrayList<StringBuilder>();
        for(int i = 0; i < numRows; i++)  rows.add(new StringBuilder());
        int i = 0, flag = -1;//flag为-1代表控制rows中字符串参数向上
        for(char c : s.toCharArray()) {
            rows.get(i).append(c);
            if(i == 0 || i == numRows -1)  flag = - flag;  // 当到达顶部或底部时，反转方向
            i += flag;
        }
        StringBuilder res = new StringBuilder();
        for(StringBuilder row : rows)  res.append(row);
        return res.toString();
    }
}