LeetCode:Valid Parentheses

 1 class Solution {
 2 public:
 3     bool isValid(string s) {
 4         int n = s.size();
 5         if(n == 0)return true;
 6         stack<char> sta;
 7         sta.push('#');
 8         for(int i = 0; i < n; i++)
 9         {
10             switch(s[i])
11             {
12                 case '(': sta.push('('); break;
13                 case '{': sta.push('{'); break;
14                 case '[': sta.push('['); break;
15                 case ')': {
16                     char top = sta.top();
17                     if(top != '(')return false;
18                     else sta.pop();
19                     break;}
20                 case '}': {
21                     char top = sta.top();
22                     if(top != '{')return false;
23                     else sta.pop();
24                     break;}
25                 case ']': {
26                     char top = sta.top();
27                     if(top != '[')return false;
28                     else sta.pop();
29                     break;}
30             }
31         }
32         if(sta.size() == 1)return true;
33         else return false;
34     }
35 };