[leetcode] Longest Valid Parentheses

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.

 

思路：传统的括号匹配方法，用堆栈去匹配，遇到'('压入;遇到')',如果栈不为空，匹配成功，弹出栈顶元素，否则匹配不成功。此题需要新加一个标识数组，匹配到的位置标注为1，未匹配到的标注为0，遍历标识数组，统计连续出现1的长度，选择最长的len即为所求结果。

class Solution
{
public:
  int longestValidParentheses(string s)
  {
    int size = s.size();
    int *is_match = new int[size];
    stack<char> my_stack;
    stack<int> temp;

    for(int i=0; i<size; i++)
    {
      if('(' == s[i])
      {
        my_stack.push('(');
        temp.push(i);
        is_match[i] = 0;
      }
      else
      {
        if(!my_stack.empty())
        {
          my_stack.pop();
          is_match[i] = 1;
          is_match[temp.top()] = 1;
          temp.pop();
        }
        else
          is_match[i] = 0;
      }
    }

    int len = 0, max = 0;
    for(int i=0; i<size; i++)
    {
      if(is_match[i] == 0)
      {
        max = max>len ? max : len;
        len = 0;
      }
      else
        len += is_match[i];

      if(i+1 == size)
        max = max>len ? max : len;
    }

    return max;
  }
};