Solution to LeetCode Problems: Valid Parentheses

Valid Parentheses

Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.
The brackets must close in the correct order, "()" and "()[]{}" are all valid but "(]" and "([)]" are not.

Thoughts:
A stack should do the job. 

Solution:

1. class Solution {  
2. public:  
3.     char counterPart(const char ch)  
4.     {  
5.         switch(ch)  
6.         {  
7.             case '{':  
8.                 return '}';  
9.             case '[':  
10.                 return ']';  
11.             case '(':  
12.                 return ')';  
13.             default:  
14.                 return 0;  
15.         }  
16.     }  
17.   
18.     bool isValid(string s) {  
19.         stack<char> parenthesis;  
20.           
21.         for(auto ch: s)  
22.             if (ch == '(' || ch == '[' || ch == '{')  
23.                 parenthesis.push(ch);  
24.             else  
25.                 if (!parenthesis.empty() && ch == counterPart(parenthesis.top()))  
26.                     parenthesis.pop();  
27.                 else  
28.                     return false;  
29.           
30.         return parenthesis.empty();  
31.     }  
32. };