LC1614. Maximum Nesting Depth of the Parentheses

class Solution:
    def maxDepth(self, s: str) -> int:
        num_open = 0
        max_depth = 0
 
        for c in s:
            if c == '(':
                num_open += 1
                max_depth = max(num_open, max_depth)
            elif c == ')':
                num_open -= 1
        
        return max_depth

Complexity

Time: $O(n)$ where $n$ is number of characters in string
Space: $O(1)$