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;
    }
}