Problem
Given a string containing just the characters '(' and ')', find the length of the longest valid (well-formed) parentheses substring.
Example 1:
Input: "(()"
Output: 2
Explanation: The longest valid parentheses substring is "()"
Example 2:
Input: ")()())" Output: 4 Explanation: The longest valid parentheses substring is"()()"
Solution: Stack
Use a stack to track the index of all unmatched open parentheses.
Time complexity: O(n)
Space complexity: O(n)
C++
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// Author: Huahua class Solution { public: int longestValidParentheses(string s) { stack<int> q; int start = 0; int ans = 0; for (int i = 0;i < s.length(); i++) { if(s[i] == '(') { q.push(i); } else { if (q.empty()) { start = i + 1; } else { int index = q.top(); q.pop(); ans = max(ans, q.empty() ? i - start + 1 : i - q.top()); } } } return ans; } }; |
Python3
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# Author: Huahua class Solution: def longestValidParentheses(self, s): q = [] start, ans = 0, 0 for i in range(len(s)): if s[i] == '(': q.append(i) continue if not q: start = i + 1 else: q.pop() ans = max(ans, i - q[-1] if q else i - start + 1) return ans |
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