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

解析

此題要判斷給定的字串是否為有效的括弧組。

解法

class Solution(object):
    def isValid(self, s):
        stack = []
        mapping = {")": "(", "}": "{", "]": "["}
        for char in s:
            if char in mapping:
                top_element = stack.pop() if stack else '#'
                if mapping[char] != top_element:
                    return False
            else:
                stack.append(char)
        return not stack

備註

希望透過記錄解題的過程，可以對於資料結構及演算法等有更深一層的想法。
如有需訂正的地方歡迎告知，若有更好的解法也歡迎留言，謝謝。