# 1

class Solution:
    def isValid(self, s: str) -> bool:

        stack = []
        mapping = {
            "(" : ")",
            "{" : "}",
            "[" : "]"
        }
        for character in s:
            if character in mapping:
                stack.append(character)
            elif character in list(mapping.values()):
                if len(stack)==0 or (mapping[stack.pop()] != character):
                    return False

        if len(stack)>0:
            return False
        else:
            return True

# 2
class Solution:
    def isValid(self, string: str) -> bool:

            stack = []
            mapping = {
                "}" : "{",
                ")" : "(",
                "]" : "["
            }

            for s in string:
                if s in ["{", "(", "["]:
                    stack.append(s)
                elif s in ["}", ")", "]"]:
                    if len(stack) > 0 and stack[-1] == mapping[s]:
                        stack.pop()
                    else:
                        return False
                else:
                    continue

            # return only if stack is empty
            return (len(stack) == 0)

# 3
# Didn't like the editorial. Skipping it.