LeetCode Longest Valid Parentheses

最新推荐文章于 2022-09-01 00:56:47 发布

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本文介绍了一种解决最长有效括号子串问题的方法。利用栈和动态规划思想，找到给定字符串中最大长度的有效括号子串。通过示例说明了如何实现这一算法。

题目：

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

class Solution {
public:
	int longestValidParentheses(string s) {
		vector<int> f(s.size(), 0);
		stack<int> t;
		int ans = 0;
		for (int i = 0; i < s.size(); i++) {
			if (s[i] == '(')
				t.push(i);
			else if (!t.empty()) {
				int k = t.top();
				t.pop();
				f[i] = i - k + 1 + (k > 0 ? f[k - 1] : 0);
				ans = max(ans, f[i]);
			}
		}
		return ans;
	}
};