LeetCode-in-All

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 {
    /**
     * @param String $s
     * @param Integer $numRows
     * @return String
     */
    public function convert($s, $numRows) {
        if ($numRows == 1) {
            return $s;
        }
        $row = 0;
        $col = 0;
        $dir = 'down';
        for ($i = 0; $i < strlen($s); $i++) {
            $string[$row][] = $s[$i];
            if ($row < $numRows - 1 && $dir == 'down') {
                $row++;
            } elseif ($row == $numRows - 1 && $dir == 'down') {
                $row--;
                $dir = 'up';
                $col++;
            } elseif ($row > 0) {
                $row--;
                $col++;
            } else {
                $dir = 'down';
                $row++;
            }
        }
        return implode(array_merge(...$string));
    }
}

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