leetcode刷题-堆栈3

package com.zwd.wkst.leetcode.stack;import java.util.Stack;/** * Created by zhangwd4 on 2017/11/2. * * Given a string containing just the characters '(', ')', '{', '}', '[' and ']', * determine if the input string is valid. The brackets must close in the correct order, "()" and "()[]{}" are all valid but "(]" and "([)]" are not. 思路： 当符号是 左边的符号 时，压入堆栈； 当符号是右边符号时：1 堆栈不为空，2 栈顶元素是相对应的左边符号;而且如果不全满足，直接返回false； 当程序运行完，栈是空，返回true */public class Solution2 {    public boolean isValid(String s) {        if(s ==null || s.isEmpty()){            return false;        }        Stack<Character> stack = new Stack<>();        for(char c : s.toCharArray()){            if(c == '(' || c== '[' || c == '{')                stack.push(c);            else if(c == ')' && !stack.empty() && stack.peek() == '(')                stack.pop();            else if(c == ']' && !stack.empty() && stack.peek() == '[')                stack.pop();            else if(c == '}' && !stack.empty() && stack.peek() == '{')                stack.pop();            else                return false;        }        return stack.isEmpty();    }}