1614. Maximum Nesting Depth of the Parentheses

Easy

A string is a valid parentheses string (denoted VPS) if it meets one of the following:

• It is an empty string "", or a single character not equal to "(" or ")",
• It can be written as AB (A concatenated with B), where A and B are VPS's, or
• It can be written as (A), where A is a VPS.

We can similarly define the nesting depth depth(S) of any VPS S as follows:

• depth("") = 0
• depth(C) = 0, where C is a string with a single character not equal to "(" or ")".
• depth(A + B) = max(depth(A), depth(B)), where A and B are VPS's.
• depth("(" + A + ")") = 1 + depth(A), where A is a VPS.

For example, "", "()()", and "()(()())" are VPS's (with nesting depths 0, 1, and 2), and ")(" and "(()" are not VPS's.

Given a VPS represented as string s, return the nesting depth of s.

Example 1:

• Input: s = "(1+(2*3)+((8)/4))+1"
• Output: 3
• Explanation: Digit 8 is inside of 3 nested parentheses in the string.

Example 2:

• Input: s = "(1)+((2))+(((3)))"
• Output: 3

Constraints:

• 1 <= s.length <= 100
• s consists of digits 0-9 and characters '+', '-', '*', '/', '(', and ')'.
• It is guaranteed that parentheses expression s is a VPS.

Solution:

class Solution {

    /**
     * @param String $s
     * @return Integer
     */
    function maxDepth($s) {
        $ans = 0;
        $opened = 0;

        foreach(str_split($s) as $c) {
            if ($c == '(') {
                $opened += 1;
                $ans = max($ans, $opened);
            } elseif ($c == ')') {
                $opened -= 1;
            }
        }

        return $ans;
    }
}

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