LeetCode-in-Cpp
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
#include <string>
#include <algorithm>
using namespace std;
class Solution {
public:
int longestValidParentheses(const string& s) {
int maxLen = 0;
int left = 0, right = 0;
int n = s.length();
// Left to right scan
for (int i = 0; i < n; ++i) {
if (s[i] == '(') {
++left;
} else {
++right;
}
if (right > left) {
left = right = 0;
}
if (left == right) {
maxLen = max(maxLen, left + right);
}
}
left = right = 0;
// Right to left scan
for (int i = n - 1; i >= 0; --i) {
if (s[i] == '(') {
++left;
} else {
++right;
}
if (left > right) {
left = right = 0;
}
if (left == right) {
maxLen = max(maxLen, left + right);
}
}
return maxLen;
}
};