LeetCode-in-Dart
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
class Solution {
int longestValidParentheses(String s) {
int max = 0;
int left = 0;
int right = 0;
int n = s.length;
late String ch;
// Left to right pass
for (int i = 0; i < n; i++) {
ch = s[i];
if (ch == '(') {
left++;
} else {
right++;
}
if (right > left) {
left = 0;
right = 0;
}
if (left == right) {
max = max > (left + right) ? max : (left + right);
}
}
left = 0;
right = 0;
// Right to left pass
for (int i = n - 1; i >= 0; i--) {
ch = s[i];
if (ch == '(') {
left++;
} else {
right++;
}
if (left > right) {
left = 0;
right = 0;
}
if (left == right) {
max = max > (left + right) ? max : (left + right);
}
}
return max;
}
}