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6. zigzag conversion

admin 11月 16, 2020 0

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)

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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:

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string convert(string s, int numRows);

Example 1:

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Input: s = "PAYPALISHIRING", numRows = 3
Output: "PAHNAPLSIIGYIR"

Example 2:

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Input: s = "PAYPALISHIRING", numRows = 4
Output: "PINALSIGYAHRPI"
Explanation:

P     I    N
A   L S  I G
Y A   H R
P     I
 
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class  {
    public String convert(String s, int nRows) {
        if (s == null || nRows == 1)
           return s;
       int len = s.length();
       if (len <= nRows)
            return s;
       StringBuffer res = new StringBuffer();
      int size = 2 * nRows - 2;
       for (int i = 0; i < nRows; i++) {//每一行的元素
          char ch;
            for (int j = i; j < len; j += size) {
               ch = s.charAt(j);
                res.append(ch);
              if (i != 0 && i != nRows - 1) {//如果是中间元素单独处理
                   int tmp = j + size - 2 * i;
                 if (tmp < len) {
                     ch = s.charAt(tmp);
                      res.append(ch);
                  }
                }
            }
        }
            return res.toString();
    }

}
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