LeetCode [20] Valid Parentheses

20. Valid Parentheses

Easy

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

Example 4:

Input: s = "([)]"
Output: false

Example 5:

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

 

Constraints:

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

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