LeetCode力扣之Longest Valid Parentheses

Given a string containing just the characters 

'('

 and 

')'

, find the length of the longest valid (well-formed) parentheses substring.For 

"(()"

, the longest valid parentheses substring is 

"()"

, which has length = 2.Another example is 

")()())"

, where the longest valid parentheses substring is 

"()()"

, which has length = 4.import java.util.Stack;

/**
* Created by lxw, liwei4939@126.com on 2018/3/6.
*/
public class LongestValidParentheses {

public int longestValidParenthese(String s){

Stack<Integer> st = new Stack<>();
int max = 0;
for (int i= 0; i < s.length(); i++){

//如果当前字符是右括号，记录栈非空且栈顶对应为左括号
if (s.charAt(i) == ')' && !st.isEmpty() && s.charAt(st.peek()) == '('){

//左括号出栈
st.pop();
//与当前右括号最近的左括号出栈后，栈要么为空，要么为右括号，要么为左括号
max = Math.max(max, i - (st.isEmpty() ? -1 : st.peek()));
}
else {
st.push(i);
}
}
return max;
}

public static void main(String[] args){
LongestValidParentheses tmp = new LongestValidParentheses();
String str = ")()())";
System.out.println(tmp.longestValidParenthese(str));
}
}
PS: JAVA 中Stack是一个古老的类，JDK文档中只有empty()方法，isEmpty()是从Vector类中继承过来的，程序中使用前者运行超时，使用后者通过