LeetCode-in-All
20. Valid Parentheses
Easy
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 <= 104sconsists of parentheses only'()[]{}'.
Solution
class Solution {
/**
* @param String $s
* @return Boolean
*/
public function isValid($s) {
$stack = [];
$length = strlen($s);
for ($i = 0; $i < $length; $i++) {
$c = $s[$i];
if ($c == '(' || $c == '[' || $c == '{') {
array_push($stack, $c);
} elseif (($c == ')' && !empty($stack) && end($stack) == '(')
|| ($c == '}' && !empty($stack) && end($stack) == '{')
|| ($c == ']' && !empty($stack) && end($stack) == '[')
) {
array_pop($stack);
} else {
return false;
}
}
return empty($stack);
}
}