20. Valid Parentheses

class Solution:
    def isValid(self, s: str) -> bool:
        stack = []
        m = {
            ')': '(',
            '}': '{',
            ']': '['
        }
        
        for c in s:
            if c in ['(', '{', '[']:
                stack.append(c)
            elif len(stack) == 0 or c in [')', '}', ']'] and stack[-1] != m[c]:
                return False
            else:
                stack.pop()
        
        return len(stack) == 0

• stack to store the brackets.
• hashmap for ease of coding.
• just loop through the string.
• edge cases for ill-formed strings (start with closing bracket, not enough closing brackets).

Categories:: stack, hashmap, string