[LeetCode] 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.

利用一个栈来保存前括号，然后有后括号来时弹出栈顶来判断

class Solution {
public:
    bool isValid(string s) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        stack<char> st;
        
        for(int i = 0; i < s.size(); i++)
            if (s[i] == ')' || s[i] == ']' || s[i] == '}')
            {
                if (st.empty())
                    return false;
                else
                {
                    char c = st.top();
                    st.pop();
                    if ((c == '(' && s[i] != ')') || (c == '[' && s[i] != ']') || (c == '{' && s[i] != '}'))
                        return false;
                }
            }
            else
                st.push(s[i]);
                
        return st.empty();
    }
};