https://oj.leetcode.com/problems/valid-parentheses/
遇到左括号入栈,遇到右括号出栈找匹配,为空或不匹配为空,
public class Solution { public boolean isValid(String s) { char c[]=s.toCharArray(); Stack<Character> stack=new Stack<Character>(); for(int i=0;i<s.length();i++) { if(c[i]=='('||c[i]=='['||c[i]=='{')stack.push(c[i]); else { if(stack.isEmpty()) return false; char c2=stack.peek(); if(c[i]==')'&&c2=='(') stack.pop(); else if(c[i]==']'&&c2=='[') stack.pop(); else if(c[i]=='}'&&c2=='{') stack.pop(); else return false; } } if(stack.isEmpty()) { return true; } return false; } }