LeetCode-in-All
10. Regular Expression Matching
Hard
Given an input string s and a pattern p, implement regular expression matching with support for '.' and '*' where:
'.'Matches any single character.'*'Matches zero or more of the preceding element.
The matching should cover the entire input string (not partial).
Example 1:
Input: s = “aa”, p = “a”
Output: false
Explanation: “a” does not match the entire string “aa”.
Example 2:
Input: s = “aa”, p = “a*”
Output: true
Explanation: ‘*’ means zero or more of the preceding element, ‘a’. Therefore, by repeating ‘a’ once, it becomes “aa”.
Example 3:
Input: s = “ab”, p = “.*”
Output: true
Explanation: “.*” means “zero or more (*) of any character (.)”.
Example 4:
Input: s = “aab”, p = “c*a*b”
Output: true
Explanation: c can be repeated 0 times, a can be repeated 1 time. Therefore, it matches “aab”.
Example 5:
Input: s = “mississippi”, p = “mis*is*p*.”
Output: false
Constraints:
1 <= s.length <= 201 <= p.length <= 30scontains only lowercase English letters.pcontains only lowercase English letters,'.', and'*'.- It is guaranteed for each appearance of the character
'*', there will be a previous valid character to match.
Solution
class Solution {
private $cache;
/**
* @param String $s
* @param String $p
* @return Boolean
*/
public function isMatch($s, $p) {
$this->cache = array_fill(0, strlen($s) + 1, array_fill(0, strlen($p) + 1, null));
return $this->isMatchHelper($s, $p, 0, 0);
}
private function isMatchHelper($s, $p, $i, $j) {
if ($j == strlen($p)) {
return $i == strlen($s);
}
if ($this->cache[$i][$j] !== null) {
return $this->cache[$i][$j];
}
$firstMatch = ($i < strlen($s)) && ($s[$i] == $p[$j] || $p[$j] == '.');
if (($j + 1) < strlen($p) && $p[$j + 1] == '*') {
$result = ($firstMatch && $this->isMatchHelper($s, $p, $i + 1, $j)) ||
$this->isMatchHelper($s, $p, $i, $j + 2);
} else {
$result = $firstMatch && $this->isMatchHelper($s, $p, $i + 1, $j + 1);
}
$this->cache[$i][$j] = $result;
return $result;
}
}