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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.
solution：用stack，复杂度O(n)
package leetcode2; import java.util.Stack; public class LongestValid_Parentheses { public static int longest_VP_DP(String s) { Stack<Integer> re =new Stack<Integer>(); int start=-1; int maxl=0; int location; for(int i=0;i<s.length();i++){ if (s.charAt(i)==‘(‘){ re.push(i); }else{ if(re.empty()){ start=i; }else{ location=re.pop(); if(re.empty()){ maxl=Math.max(maxl, i-start); //外围没有(括号了，到i已得到一个局部最大值 }else{ maxl=Math.max(maxl, re.peek()-i); //外围还有（，没有结束哦 } } } } return maxl; } public static void main(String[] args) { // TODO Auto-generated method stub String string="()()("; System.out.println(longest_VP_DP(string)); } }
Leetcode32. Longest Valid Parentheses
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原文地址：http://www.cnblogs.com/joannacode/p/4389328.html
