Longest Valid Paranthesis
~3 mins read
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
def longestValidParentheses(self, s: str) -> int:
maxlen = 0
l = r = 0
for c in s:
if c == "(":
l += 1
else:
r += 1
if l == r:
maxlen = max(maxlen, 2 * l)
elif r > l:
l = r = 0
l = r = 0
for c in reversed(s):
if c == ")":
l += 1
else:
r += 1
if l == r:
maxlen = max(maxlen, 2 * l)
elif r > l:
l = r = 0
return maxlen
assert longestValidParentheses("()()())") == 4
assert longestValidParentheses("(()") == 2
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
/*
Input: ")()())"
Output: 4
Explanation: The longest valid parentheses substring is "()()"
*/
// stack, linear time and space
public int longestValidParentheses(String s) {
int maxans = 0;
Stack<Integer> stack = new Stack<>();
stack.push(-1);
for (int i = 0; i < s.length(); i++) {
if (s.charAt(i) == '(') {
stack.push(i);
} else {
stack.pop();
if (stack.empty()) {
stack.push(i);
} else {
maxans = Math.max(maxans, i - stack.peek());
}
}
}
return maxans;
}