Given a string 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.

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 方法一：hashmap+栈

class Solution {    public static boolean isValid(String s) {        HashMap
     
       map=new HashMap
      
       ();        Stack
       
         stack=new Stack
        
         ();        map.put(')','(');        map.put(']','[');        map.put('}','{');        int N=s.length();        char [] nums=s.toCharArray();        for(int i=0;i
        
       
      
     

方法二：栈

class Solution {    public static boolean isValid(String s) {        Stack
     
       stack=new Stack
      
       ();          int N=s.length();        char [] nums=s.toCharArray();        for(int i=0;i