LeetCode 20. 有效的括号 Java

就是栈。用map存储括号类型，遇到右括号弹栈，不匹配为false。左括号压栈。

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