有效括号

class Solution {
    
    private HashMap<Character, Character> hashMap;
    
    public Solution()
    {
        this.hashMap=new HashMap<Character, Character>();
        this.hashMap.put(‘)‘, ‘(‘);
        this.hashMap.put(‘}‘, ‘{‘);
        this.hashMap.put(‘]‘, ‘[‘);
    }
    
    public boolean isValid(String s) {
        
        Stack<Character> stack=new Stack<>();
        
        for(int i=0;i<s.length();i++)
        {
            char c=s.charAt(i);
            
            if(this.hashMap.containsKey(c))
            {
                char topElement=stack.empty()? ‘#‘:stack.pop();
                if(topElement!=this.hashMap.get(c))
                {
                    return false;
                }
            }
            else {
                stack.push(c);
            }
        }
        
        return stack.empty();
    }
}