LeetCode 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.

题意：找到最长的合法串的长度

思路：dp的思想，用d[i]表示从第i个位置开始匹配的长度，那么对于第i个来说，如果它是右括号的话，那么这个位置就是0，如果是做括号的话，那么就要跳过第i+1匹配的最长长度的位置来到j，看位置j是不是右括号，其次还要加上位置j+1的位置的匹配长度。

class Solution {public:    int longestValidParentheses(string s) {        if (s.length() == 0) return 0;        int ans = 0;        int *d = new int[s.length()];        for (int i = 0; i < s.length(); i++)            d[i] = 0;        d[s.length() - 1] = 0;        for (int i = s.length() - 2; i >= 0; i--) {            if (s[i] == ')')                 d[i] = 0;            else {                int j = i + 1 + d[i + 1];                if (j < s.length() && s[j] == ')') {                    d[i] = d[i+1] + 2;                    if (j + 1 < s.length())                         d[i] += d[j+1];                }            }            ans = max(ans, d[i]);        }        return ans;    }};