Leetcode题目20.有效的括号（简单）

package com.company;

import java.util.LinkedList;

public class Main {

    public static void main(String[] args) {
        String str = "]";
        System.out.println(isValid(str));
    }

    private static boolean isValid(String s) {
        if (s == null || s.isEmpty()) {
            return true;
        }
        LinkedList<Character> linkedList = new LinkedList<>();
        for (int i = 0; i < s.length(); i++) {
            char ch = s.charAt(i);
            if (ch == ‘(‘ || ch == ‘[‘ || ch == ‘{‘) {
                linkedList.add(ch);
            } else {
                //栈中没有元素，而当前符号为右括号，直接返回false,当前符号也不需要进栈
                if (linkedList.isEmpty()) {
                    return false;
                }
                if (ch == ‘)‘) {
                    if (linkedList.peekLast() != ‘(‘) {
                        return false;
                    }
                }
                if (ch == ‘]‘) {
                    if (linkedList.peekLast() != ‘[‘) {
                        return false;
                    }
                }
                if (ch == ‘}‘) {
                    if (linkedList.peekLast() != ‘{‘){
                        return false;
                    }
                }
                if (!linkedList.isEmpty()) {
                    linkedList.removeLast();
                }
            }
        }
        return linkedList.isEmpty();
    }
}