32. Longest Valid Parentheses

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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.

package leetcode;public class leet32 {public static void main(String[] args) {leet32 leet = new leet32();int result = leet.longestVaildParentheses("((())");System.out.println(result);}public int longestVaildParentheses(String s){StringBuilder str = new StringBuilder();for(int i = 0;i < s.length();i++){if(s.charAt(i) == '('){str.append(s.charAt(i));}else{if(str.length() == 0){str.append(s.charAt(i));}else if(str.substring(str.length()-1).equals("(")){String tmp = str.substring(0, str.length()-1);str = new StringBuilder().append(tmp);}else{str.append(s.charAt(i));}}}return s.length()-str.length();}}

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