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Valid Parentheses

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

An input string is valid if:

Open brackets must be closed by the same type of brackets.

Open brackets must be closed in the correct order.

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

class Solution(object):
    def isValid(self, s):
        stack = [] # create an empty stack to store opening brackets
        for c in s: # loop through each character in the string
            if c in '([{': # if the character is an opening bracket
                stack.append(c) # push it onto the stack
            else: # if the character is a closing bracket
                if not stack or \
                    (c == ')' and stack[-1] != '(') or \
                    (c == '}' and stack[-1] != '{') or \
                    (c == ']' and stack[-1] != '['):
                    return False # the string is not valid, so return false
                stack.pop() # otherwise, pop the opening bracket from the stack
        return not stack # if the stack is empty, all opening brackets have been matched with their corresponding closing brackets,
                         # so the string is valid, otherwise, there are unmatched opening brackets, so return false

Posted by Jamie Meyer 4 months ago

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