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32. Longest Valid Parentheses
Hard
Given a string containing just the characters '(' and ')', find the length of the longest valid (well-formed) parentheses substring.
Example 1:
Input: s = “(()”
Output: 2
Explanation: The longest valid parentheses substring is “()”.
Example 2:
Input: s = “)()())”
Output: 4
Explanation: The longest valid parentheses substring is “()()”.
Example 3:
Input: s = “”
Output: 0
Constraints:
0 <= s.length <= 3 * 104s[i]is'(', or')'.
Solution
object Solution {
@SuppressWarnings(Array("scala:S3776"))
def longestValidParentheses(s: String): Int = {
var max = 0
var left = 0
var right = 0
val n = s.length
for (i <- 0 until n) {
val ch = s.charAt(i)
if (ch == '(') {
left += 1
} else {
right += 1
}
if (right > left) {
left = 0
right = 0
}
if (left == right) {
max = math.max(max, left + right)
}
}
left = 0
right = 0
for (i <- n - 1 to 0 by -1) {
val ch = s.charAt(i)
if (ch == '(') {
left += 1
} else {
right += 1
}
if (left > right) {
left = 0
right = 0
}
if (left == right) {
max = math.max(max, left + right)
}
}
max
}
}