20. Valid Parentheses

Problem Link

Description

---

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.
3. Every close bracket has a corresponding open bracket of the same type.

 

Example 1:

Input: s = "()"

Output: true

Example 2:

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

Output: true

Example 3:

Input: s = "(]"

Output: false

Example 4:

Input: s = "([])"

Output: true

 

Constraints:

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

Solution

---

Python3

class Solution:
    def isValid(self, s: str) -> bool:
        mp = {")" : "(", "}" : "{", "]" : "["}
        stack = []
 
        for x in s:
            if x in mp:
                if stack and stack[-1] == mp[x]:
                    stack.pop()
                else:
                    return False
            else:
                stack.append(x)
 
        return len(stack) == 0