LeetCode:Longest Valid Parentheses

Longest Valid Parentheses

Total Accepted: 63715 Total
Submissions: 282480 Difficulty: Hard

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.

Subscribe to see which companies asked this question

Hide Tags
Dynamic Programming String

Hide Similar Problems
(E) Valid Parentheses

思路：

使用stack来保存未匹配的“括号”的下标，然后求下标之间的最大差值。

c++ code:

class Solution {
public:
int longestValidParentheses(string s) {
int n = s.length();
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);
}
}

int a = n, b = 0;
int ans = 0;
while(!st.empty()) {
b = st.top();
st.pop();
ans = max(ans, a-b-1);
a = b;
}
ans = max(ans, a);
return ans;
}
};