Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.
An input string is valid if:
- Open brackets must be closed by the same type of brackets.
- Open brackets must be closed in the correct order.
Example 1:
Input: s = "()"
Output: true
Example 2:
Input: s = "()[]{}"
Output: true
Example 3:
Input: s = "(]"
Output: false
Example 4:
Input: s = "([)]"
Output: false
Example 5:
Input: s = "{[]}"
Output: true
Constraints:
- 1 <= s.length <= 104
- s consists of parentheses only '()[]{}'.
class Solution {
/**
* @param String $s
* @return Boolean
*/
function isValid($s) {
$lookup = ['(' => ')', '[' => ']' ,'{' => '}'];
$stack = [];
$sLength = strlen($s);
if (! $sLength || $sLength % 2 !== 0) {
return false;
}
for ($i = 0; $i < $sLength; $i++) {
if (array_key_exists($s[$i], $lookup)) {
array_push($stack, $s[$i]);
} else {
$bracket = count($stack) ? array_pop($stack) : '';
if ($lookup[$bracket] !== $s[$i]) {
return false;
}
}
}
return ! count($stack);
}
}