isValid 【有效的括号】

stack

public boolean isValid(String s) {
        Map<Character,Character> map = new HashMap<>();
        map.put(')','(');
        map.put(']','[');
        map.put('}','{');

        Stack<Character> stack = new Stack<>();
        for(int i=0;i<s.length();i++){
            if(stack.isEmpty()){
                stack.push(s.charAt(i));
            }else{
                if(stack.peek() == map.get(s.charAt(i))){
                    stack.pop();
                }else{
                    stack.push(s.charAt(i));
                }
            }
        }
        return stack.isEmpty();
    }