0020_Valid Parentheses

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.

JAVA

直接使用栈来做，不过之前在看书的时候，好像说java中的栈被取代了？？？记不清了，这次先用栈做一下，下次去书中找一下看看是不是自己记错了。时间复杂度

O(N)

效率排名在中间，可以考虑优化一下。

public class Solution {    public boolean isValid(String s) {        if(s.length() % 2 != 0){            return false;        }        Stack<Character> sta = new Stack<Character>();        char temp;        for(int i = 0; i < s.length();++i){            temp = s.charAt(i);            if(sta.empty()){                sta.push(temp);            }else {                switch (temp){                    case '(':                    case '[':                     case '{':                        sta.push(temp);                        break;                    case ')':                        if(sta.peek() == '('){                            sta.pop();                        }else{                            return false;                        }                        break;                    case ']':                        if(sta.peek() == '['){                            sta.pop();                        }else{                            return false;                        }                        break;                    case '}':                        if(sta.peek() == '{'){                            sta.pop();                        }else{                            return false;                        }                        break;                }            }        }        if(sta.empty()){            return true;        }        return false;    }}