Question 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.

Examples

Example 1

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Input: s = "()"
Output: true

Example 2

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

Example 3

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Input: s = "(]"
Output: false

Constraints

  • 1 <= s.length <= $10^4$
  • s consists of parentheses only '()[]{}'.

Thoughts

Solution

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class Solution:
    def isValid(self, s: str) -> bool:
        stack = []
        l_paren = ['(', '[', '{']
        r_paren = [')', ']', '}']

        for i in s:
            if i in l_paren:
                stack.append(i)
            if i in r_paren:
                if len(stack) == 0:
                    return False
                latest = stack.pop()
                if r_paren[l_paren.index(latest)] != i:
                    return False
        if len(stack) > 0:
            return False
        else:
            return True