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1614. Maximum Nesting Depth of the Parentheses

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

Example 3:

Input: s = "1+(2*3)/(2-1)"
Output: 1

Example 4:

Input: s = "1"
Output: 0

Constraints:

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

Solutions (Ruby)

1. Count

# @param {String} s
# @return {Integer}
def max_depth(s)
  left_count = 0
  ret = 0

  s.chars.each do |ch|
    if ch == '('
      left_count += 1
      ret = left_count if left_count > ret
    elsif ch == ')'
      left_count -= 1
    end
  end

  ret
end

Solutions (Rust)

1. Count

impl Solution {
    pub fn max_depth(s: String) -> i32 {
        let mut left_count = 0;
        let mut ret = 0;

        for ch in s.chars() {
            match ch {
                '(' => {
                    left_count += 1;
                    ret = ret.max(left_count);
                }
                ')' => left_count -= 1,
                _ => (),
            }
        }

        ret
    }
}