[Title] LeetCode brush stack stack-- effective brackets

topic 

Includes only a given '(', ')' string, '{', '}', '[', ']', and determine whether the string is valid.

Valid string must meet:

Left bracket must be closed by a closing parenthesis of the same type.
Left parenthesis must be closed in the correct order.
Note the empty string can be considered a valid string.

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

 code:

class Solution:
    def isValid(self, s):
        # 字典dic保存有效括号对，key：value
        dic = {'{': '}',  '[': ']', '(': ')', '?': '?'}
        stack = ['?']
        for c in s:
            if c in dic:
                stack.append(c)
            elif dic[stack.pop()] != c:
                return False
        return len(stack) == 1

a = Solution()
s = a.isValid("{[([])]}")
print(s)

•  pop () function is used to remove the value of an element in the list (default to the last element), and returns the element.