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.

A: 用栈模拟

bool isOpenBracket(char c)
{
    if(c=='('||c=='['||c=='{')
        return true;
    else return false;
}
class Solution {
public:
    bool isValid(string s) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        // use stack
        stack<char> st;
        for(int i=0;i<s.size();i++)
        {
            if(isOpenBracket(s[i]))
                st.push(s[i]);
            else 
            {
                if(st.empty())
                    return false;
                char c = st.top();
                st.pop();
                if((s[i]==')'&&c=='(')||(s[i]==']'&&c=='[')||(s[i]=='}'&&c=='{'))
                    continue;
                else
                    return false;
            }
        }
        
        return st.empty();
        
    }
};