'''
Given a string 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.
Note that an empty string is also considered valid.
Example 1:
Input: "()"
Output: true
Example 2:
Input: "()[]{}"
Output: true
Example 3:
Input: "(]"
Output: false
Example 4:
Input: "([)]"
Output: false
Example 5:
Input: "{[]}"
Output: true
'''
class Solution:
    def isValid(self, s):
        """
        :type s: str
        :rtype: bool
        """
        stack = []
        map = {'{':'}','(':')','[':']'}
        for ch in s:
            if ch in map:
                stack.append(ch)
            elif stack != []:
                popped = stack.pop()
                if map[popped] != ch:
                    return False
            else:
                return False
        if stack == []:
            return True
        else:
            return False
