32. Longest Valid Parentheses
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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"()()"
AC code:
class Solution {
public:
int longestValidParentheses(string s) {
int n = s.length(), longest = 0;
stack<int> st;
for (int i = 0; i < n; i++) {
if (s[i] == ‘(‘) st.push(i);
else {
if (!st.empty()) {
if (s[st.top()] == ‘(‘) st.pop();
else st.push(i);
}
else st.push(i);
}
}
if (st.empty()) longest = n;
else {
int a = n, b = 0;
while (!st.empty()) {
b = st.top(); st.pop();
longest = max(longest, a-b-1);
a = b;
}
longest = max(longest, a);
}
return longest;
}
};
Runtime: 8 ms, faster than 62.98% of C++ online submissions for Longest Valid Parentheses.
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