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Tested Python solution for LeetCode 20 with 20 pytest cases. Generate a practice environment with lcpy.
lcpy gen -n 20 # by problem number
lcpy gen -s valid_parentheses # by problem name
s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.
An input string is valid if:
Input: s = "()"
Output: true
Input: s = "()[]{}"
Output: true
Input: s = "(]"
Output: false
Input: s = "([])"
Output: true
Input: s = "([)]"
Output: false
1 <= s.length <= 10^4s consists of parentheses only '()[]{}'.class Solution:
# Time: O(n)
# Space: O(n)
def is_valid(self, s: str) -> bool:
stack = []
pairs = {"(": ")", "[": "]", "{": "}"}
for char in s:
if char in pairs:
stack.append(char)
elif not stack or pairs[stack.pop()] != char:
return False
return not stack
| Time | Space |
|---|---|
| O(n) | O(n) |