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77 lines
1.3 KiB
Python
77 lines
1.3 KiB
Python
"""
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20. Valid Parentheses
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Difficulty: Easy
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https://leetcode.com/problems/valid-parentheses/
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──────────────────────────────────────────────────
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Given a string s containing just the characters '(', ')', '{', '}',
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'[' and ']', determine if the input string is valid.
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An input string is valid if:
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• Open brackets must be closed by the same type of brackets.
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• Open brackets must be closed in the correct order.
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• Every close bracket has a corresponding open bracket of the same
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type.
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Example 1:
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Input: s = "()"
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Output: true
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Example 2:
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Input: s = "()[]{}"
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Output: true
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Example 3:
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Input: s = "(]"
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Output: false
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Example 4:
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Input: s = "([])"
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Output: true
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Example 5:
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Input: s = "([)]"
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Output: false
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Constraints:
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• 1 <= s.length <= 10^4
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• s consists of parentheses only '()[]{}'.
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"""
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class Solution:
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def isValid(self, s: str) -> bool:
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stack = []
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pairs = {")": "(", "]": "[", "}": "{"}
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for c in s:
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if c in pairs:
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if stack and pairs[c] == stack[-1]:
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stack.pop()
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else:
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return False
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else:
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stack.append(c)
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return True if not stack else False
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