20. 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.

class Solution {
public:
bool isValid(string s) {
if (s.empty()) return true;
int cnt = s.size();
stack<char> temp;
for(int i = 0; i < cnt; ++i)
{
if(s[i] == '(' || s[i] == '{' || s[i] == '[')
temp.push(s[i]);
else
{
if(temp.empty())
return false;
if(s[i] == ')' && temp.top() == '(' || s[i] == '}' && temp.top() == '{' || s[i] == ']' && temp.top() == '[')
temp.pop();
else
return false;
}

}
return (temp.empty());
}
};