Java for LeetCode 032 Longest Valid Parentheses

標籤：

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.

解題思路：

本題方法多多，是Java for LeetCode 020 Valid Parentheses題目的延續，因此，我們繼續用棧的思路解決這個問題，其中需要一個index來維護最後一個‘)‘出現的位置。JAVA代碼如下：

static public int longestValidParentheses(String s) {int maxLength = 0,index=-1;Stack<Integer> stack = new Stack<Integer>();for (int i = 0; i < s.length(); i++) {if (s.charAt(i) == ‘(‘)stack.push(i);else {if(stack.empty())index=i;else{stack.pop();if(stack.isEmpty())maxLength = Math.max(maxLength, i - index);else maxLength=Math.max(maxLength, i - stack.peek());}}}return maxLength;}

 

Java for LeetCode 032 Longest Valid Parentheses