Sergio Alves

Given two strings s and t, return true if s is a subsequence of t, or false otherwise.

A subsequence of a string is a new string that is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (i.e., "ace" is a subsequence of "abcde" while "aec" is not).

Example 1:

Input: s = "abc", t = "ahbgdc"
Output: true

Example 2:

Input: s = "axc", t = "ahbgdc"
Output: false

Constraints:

• 0 <= s.length <= 100
• 0 <= t.length <= 104
• s and t consist only of lowercase English letters.

PHP Code

class Solution {

    /**
     * @param String $s
     * @param String $t
     * @return Boolean
     */
    function isSubsequence($s, $t) {
        $as = str_split($s);
        $at = str_split($t);

        if (count($as) > count($at)) {
            return false;
        }

        $n = 0;
        $s_count = 0;
        for($i=0; $i<count($as); $i++) {
            for($j=$n; $j<count($at); $j++) {
                if ($as[$i] == $at[$j]) {
                    $n = $j+1;
                    $s_count++;
                    break;
                }
                if ($j+1 == count($at)) {
                    return false;
                }
            }
        }
        if ($s_count == count($as)) {
            return true;
        }
        return false;
    }
}