DivideStringIntoGroupsOfSizeK.php

<?php

namespace App;

/**
 * Divide a String Into Groups of Size k
 *
 * A string s can be partitioned into groups of size k using the following procedure:
 * - The first group consists of the first k characters of the string, the second group consists of the next k
 * characters of the string, and so on. Each character can be a part of exactly one group.
 * - For the last group, if the string does not have k characters remaining, a character fill is used to complete the
 * group.
 * Note that the partition is done so that after removing the fill character from the last group (if it exists) and
 * concatenating all the groups in order, the resultant string should be s.
 * Given the string s, the size of each group k and the character fill, return a string array denoting the composition
 * of every group s has been divided into, using the above procedure.
 *
 * Example 1:
 * Input: s = "abcdefghi", k = 3, fill = "x"
 * Output: ["abc","def","ghi"]
 * Explanation:
 * The first 3 characters "abc" form the first group.
 * The next 3 characters "def" form the second group.
 * The last 3 characters "ghi" form the third group.
 * Since all groups can be completely filled by characters from the string, we do not need to use fill.
 * Thus, the groups formed are "abc", "def", and "ghi".
 *
 * Example 2:
 * Input: s = "abcdefghij", k = 3, fill = "x"
 * Output: ["abc","def","ghi","jxx"]
 * Explanation:
 * Similar to the previous example, we are forming the first three groups "abc", "def", and "ghi".
 * For the last group, we can only use the character 'j' from the string. To complete this group, we add 'x' twice.
 * Thus, the 4 groups formed are "abc", "def", "ghi", and "jxx".
 *
 * https://leetcode.com/problems/divide-a-string-into-groups-of-size-k
 */
class DivideStringIntoGroupsOfSizeK
{
    /**
     * @param string $str
     * @param int $k
     * @param string $fill
     * @return string[]
     */
    public function divideString(string $str, int $k, string $fill): array
    {
        $result = [];
        $strLength = strlen($str);
        $fillCount = 0;
        $group = '';
        for ($i = 0; $i < $strLength; $i++) {
            $group .= $str[$i];
            if (($i + 1) % $k === 0) {
                $result[] = $group;
                $group = '';
            }
        }
        if ($group !== '') {
            $fillCount = $k - strlen($group);
            $group .= str_repeat($fill, $fillCount);
            $result[] = $group;
        }
        if ($fillCount > 0) {
            $result[count($result) - 1] = substr($result[count($result) - 1], 0, $k);
        }
        return $result;
    }
}