leetcode刷题-堆栈2

package com.zwd.wkst.leetcode.stack;

import java.util.Stack;

/**
 * Created by zhangwd4 on 2017/11/2.
 *
 * 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
 *
 * 题目大概意思就是给你一个字符串只有 “(”和“)”，求最长的开闭ok的括号组的字符串长度。
 *
 *
 *
 */
public class Solution1 {
    public int longestValidParentheses(String s) {
        int max =0;
        if( s== null || s.isEmpty()) {
            return max;
        }
        Stack stack = new Stack<>();
        int temp = 0;
        for(int i = 0; i < s.length(); i++){
            char c = s.charAt(i);
            if(c == '('){
                stack.push(c);
            }
            else{
                if(stack.empty()){
                    temp = 0;
                    continue;
                }
                else{
                    stack.pop();
                    temp+=2;
                }
            }
            System.out.println(i+","+temp);
            max = Math.max(temp,max);
        }
        return max;
    }


    public static void main(String arg[]){
        int i = new Solution1().longestValidParentheses("()(()(()(()(()(()(()");
        System.out.println(i);
    }
}

这是我最初的版本：把问题看的有点简单了，一口气就写完了，漏洞百出啊。。。。。。。！！！！！

接下来我们来修改一下：

package com.zwd.wkst.leetcode.stack;

import java.util.ArrayList;
import java.util.List;
import java.util.Stack;

/**
 * Created by zhangwd4 on 2017/11/2.
 *
 * 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
 *
 * 题目大概意思就是给你一个字符串只有 “(”和“)”，求最长的开闭ok的括号组的字符串长度。
 *
 *
 *
 */
public class Solution1 {
    public int longestValidParentheses(String s) {
        int max =0;
        if( s== null || s.isEmpty()) {
            return max;
        }
        Stack stack = new Stack<>();
        int pos = -1;
        for(int i = 0; i < s.length(); i++){
           char c = s.charAt(i);
           if(c == '('){
               stack.push(i);
           }
           else{
               if(stack.isEmpty()){
                   pos = i;
               }
               else{
                   stack.pop();
                   if(stack.isEmpty()){
                       max = Math.max(max,i-pos);
                   }
                   else{
                       max=Math.max(max,i-stack.peek());
                   }
               }
           }
        }
        return max;
    }
    public static void main(String arg[]){
        int i = new Solution1().longestValidParentheses("()(((()");
        System.out.println(i);
    }
}