1249. Minimum Remove to Make Valid Parentheses

1249. Minimum Remove to Make Valid Parentheses

Medium

Given a string s of '(' , ')' and lowercase English characters.

Your task is to remove the minimum number of parentheses ( '(' or ')', in any positions ) so that the resulting parentheses string is valid and return any valid string.

Formally, a parentheses string is valid if and only if:

• It is the empty string, contains only lowercase characters, or
• It can be written as AB (A concatenated with B), where A and B are valid strings, or
• It can be written as (A), where A is a valid string.

Example 1:

• Input: s = "lee(t(c)o)de)"
• Output: "lee(t(c)o)de"
• Explanation: "lee(t(co)de)" , "lee(t(c)ode)" would also be accepted.

Example 2:

• Input: s = "a)b(c)d"
• Output: "ab(c)d"

Example 3:

• Input: s = "))(("
• Output: ""
• Explanation: An empty string is also valid.

Constraints:

• 1 <= s.length <= 105
• s[i] is either'(' , ')', or lowercase English letter.

Solution:

class Solution {

    /**
     * @param String $s
     * @return String
     */
    function minRemoveToMakeValid($s) {
        $stack = [];
        $openCount = 0;

        for ($i = 0; $i < strlen($s); $i++) {
            $char = $s[$i];
            if ($char == ')' && $openCount == 0) {
                continue;
            }

            if ($char == '(') {
                $openCount++;
            } elseif ($char == ')') {
                $openCount--;
            }
            $stack[] = $char;
        }

        $openCount = 0;
        $answer = [];
        for ($i = count($stack) - 1; $i >= 0; $i--) {
            $char = $stack[$i];
            if ($char == '(' && $openCount == 0) {
                continue;
            }
            if ($char == ')') {
                $openCount++;
            } elseif ($char == '(') {
                $openCount--;
            }
            $answer[] = $char;
        }
        return implode('', array_reverse($answer));
    }
}

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