Oct-11-2018

争取每周做五个LeedCode题，定期更新，难度由简到难

Title: Valid Parentheses

Description:

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:

Input: "()"
Output: true

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

Input: "(]"
Output: false

Input: "([)]"
Output: false

Input: "{[]}"
Output: true

Difficulty:

Easy

Implement Programming Language:

C#

Answer:

这道题又让我学习了新知识，栈，这个可以用典型的栈来处理，把左括号放进去，每次遇到右括号，取出来栈顶元素，看看是不是对应的，不是就错了，是就继续循环，LeedCode的Solution，很棒的思路。

public static bool IsValid(string s)
        {
            if (string.IsNullOrEmpty(s) || s.Length % 2 != 0)
                return false;
            var stack = new Stack<char>();
            for (int i = 0; i < s.Length; i++)
            {
                if (matchValue.ContainsKey(s[i]))
                {
                    if (stack.Peek() != matchValue[s[i]])
                        return false;
                    stack.Pop();
                }
                else
                {
                    stack.Push(s[i]);
                }
            }
            return stack.Count == 0;
        }

这里

Github