C++

1/**
2 * Runtime: 0 ms, faster than 100.00%
3 * Memory Usage: 6.5 MB, less than 22.49% 
4 */
5class Solution {
6  public:
7    int maxDepth(string s) {
8      int max = 0;
9      int cnt = 0;
10
11      for(int i=0; i<s.size(); ++i)
12      {
13        if (s[i] == '(') 
14        {
15          ++cnt;
16        }
17        else if (s[i] == ')')
18        {
19          --cnt;
20        }
21
22        if (cnt > max) 
23          max = cnt;
24      }
25
26      return max;
27    }
28};

JavaScript

1/**
2 * Runtime: 88 ms, faster than 23.24%
3 * Memory Usage: 38.4 MB, less than 92.83%
4 */
5var maxDepth = function(s) {
6  let cnt = 0
7  let max = 0
8
9  for (let i=0; i<s.length; ++i) {
10    if (s[i] == '(') ++cnt;
11    else if(s[i] == ')') --cnt;
12
13    max = (cnt > max) ? cnt : max;
14  }
15
16  return max;
17};

Ruby

1# Runtime: 48 ms, faster than 94.92%
2# Memory Usage: 209.9 MB, less than 64.41%
3def max_depth(s)
4  max = 0
5  cnt = 0
6
7  for i in (0...s.size) do 
8    if s[i] == '('
9      cnt += 1
10    elsif s[i] == ')'
11      cnt -= 1
12    end
13
14    max = (cnt > max) ? cnt : max
15  end
16  max
17end