Q1:Valid Parentheses

 1 class Solution {
 2 public:
 3     bool isValid(string s) {
 4         char stack[s.size()];
 5         int i = 0;
 6         int j = 0;
 7         
 8         //cout << s;
 9         
10         if(s[j] == ‘)‘ || s[j] == ‘]‘ || s[j] ==‘}‘)
11             return false;
12         else if(s[j] == ‘\0‘)
13             return true;
14         else
15             stack[i++] = s[j++];
16     
17         while(1)
18         {
19             switch(s[j])
20             {
21                 case ‘\0‘:
22                     if(i == 0)
23                         return true;
24                     else 
25                         return false;
26                 case ‘)‘:
27                     if(stack[i-1] != ‘(‘)
28                         return false;
29                     else
30                     {
31                         i -= 1;
32                         j += 1;
33                     }
34                     break;
35                 case ‘]‘:
36                     if(stack[i-1] != ‘[‘)
37                         return false;
38                     else
39                     {
40                         i -= 1;
41                         j += 1;
42                     }
43                     break;
44                 case ‘}‘:
45                     if(stack[i-1] != ‘{‘)
46                         return false;
47                     else
48                     {
49                         i -= 1;
50                         j += 1;
51                     }
52                     break;
53                 default:
54                     stack[i++] = s[j++];
55                     break;
56             }
57         }
58     }
59 };