LeetCode-in-Dart

6. Zigzag Conversion

Medium

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 s, int numRows);

Example 1:

Input: s = “PAYPALISHIRING”, numRows = 3

Output: “PAHNAPLSIIGYIR”

Example 2:

Input: s = “PAYPALISHIRING”, numRows = 4

Output: “PINALSIGYAHRPI”

Explanation: P I N A L S I G Y A H R P I

Example 3:

Input: s = “A”, numRows = 1

Output: “A”

Constraints:

• 1 <= s.length <= 1000
• s consists of English letters (lower-case and upper-case), ',' and '.'.
• 1 <= numRows <= 1000

Solution

class Solution {
  String convert(String s, int numRows) {
    int sLen = s.length;
    if (numRows == 1) {
      return s;
    }
    int maxDist = numRows * 2 - 2;
    StringBuffer buf = StringBuffer();

    for (int i = 0; i < numRows; i++) {
      int index = i;
      if (i == 0 || i == numRows - 1) {
        while (index < sLen) {
          buf.write(s[index]);
          index += maxDist;
        }
      } else {
        while (index < sLen) {
          buf.write(s[index]);
          index += maxDist - i * 2;
          if (index >= sLen) {
            break;
          }
          buf.write(s[index]);
          index += i * 2;
        }
      }
    }
    return buf.toString();
  }
}

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