Valid Parentheses (#20 Leetcode)

 Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

An input string is valid if:

1. Open brackets must be closed by the same type of brackets.
2. Open brackets must be closed in the correct order.

 

Example 1:

Input: s = "()"
Output: true

Example 2:

Input: s = "()[]{}"
Output: true

Example 3:

Input: s = "(]"
Output: false

 

Constraints:

• 1 <= s.length <= 104
• s consists of parentheses only '()[]{}'.

class Solution {
public:
    bool isValid(string s) {
        stack<char> st;
        
        for (auto c: s) {
            if (c == '(' || c == '{' || c == '[' ) {
                st.push(c);
            } else if (st.empty() || 
                       st.top() == '(' && c != ')' || 
                       st.top() == '{' &&  c != '}'|| 
                       st.top() == '[' && c != ']') {
                return false;
            } else {
                st.pop();
            }
            
        }
        return st.empty();
    }
};