【LeetCode】C# 20、Valid Parentheses

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

The brackets must close in the correct order, “()” and “()[]{}” are all valid but “(]” and “([)]” are not.

给定一个字符串，只包含括号类的符号，判断是否每个括号都为closed，是否都符合语法。

解题关键在利用堆栈后进先出的特性。看是否每个左括号都有对应的右括号

public class Solution {
public bool IsValid(string s) {
Stack<Char> stack = new Stack<Char>();
for (int i = 0; i < s.Length; i++)
{
Console.WriteLine(s[i]);
if (s.Length == 0) return false;
if (s[i] == '(')
{
stack.Push(')');
}
else if (s[i] == '{')
{
stack.Push('}');
}
else if (s[i] == '[')
{
stack.Push(']');
}
else if (stack.Count == 0)
return false;
else if (s[i] == stack.Peek())
{
stack.Pop();Console.WriteLine("pop");
}
else
return false;
}
if (stack.Count == 0)
return true;
return false;
}
}