# 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(object):
    def isValid(self, s):
        """
        :type s: str
        :rtype: bool
        """
        dict = {')':'(',']':'[','}':'{'}
        stack = []
        for ch in s:
            if ch in dict.values():
                stack.append(ch)
            elif ch in dict.keys():
                if len(stack) == 0 or (stack.pop() != dict[ch]):
                    return False
        return len(stack) == 0

def main():
    s = Solution()
    print(s.isValid("()"))
    print(s.isValid("()[]{}"))
    print(s.isValid("(]"))
    print(s.isValid("([)]"))
    print(s.isValid("{[]}"))

if __name__ == "__main__":
    main()

[]