020-valid-parentheses.py

"""
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
"""
classSolution:
defisValid(self, s: str) ->bool:
stack= []
d= {
')': '(',
'}': '{',
']': '['
 }
forcins:
ifcind.values():
stack.append(c)
elif (notstack) or (stack.pop() !=d[c]):
returnFalse
returnlen(stack) ==0