Leetcode 20. Valid Parentheses

Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

An input string is valid if:

1. Open brackets must be closed by the same type of brackets.

2. Open brackets must be closed in the correct order.

3. Every close bracket has a corresponding open bracket of the same type.

Example 1:

Input: s = "()"Output: true

Example 2:

Input: s = "()[]{}"Output: true

Example 3:

Input: s = "(]"Output: false

Constraints:

• 1 <= s.length <= 104

• s consists of parentheses only '()[]{}'.

easy 题目，其实用stack来做，速度会提高很多的。

Runtime: 186 ms, faster than 5.93% of Java online submissions for Valid Parentheses.

Memory Usage: 42.9 MB, less than 5.76% of Java online submissions for Valid Parentheses.