Java for LeetCode 032 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.

解题思路：

本题方法多多，是Java for LeetCode 020 Valid Parentheses题目的延续，因此，我们继续用栈的思路解决这个问题，其中需要一个index来维护最后一个')'出现的位置。JAVA代码如下：

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;
	}