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 * 104
- s[i] is '(', or ')'.
class Solution {
public int longestValidParentheses(String s) {
Stack<Integer> stack = new Stack<>();
stack.push(-1);
int maxLen = 0;
for(int i=0;i<s.length();i++){
if(s.charAt(i)=='('){
stack.push(i);
}else{
stack.pop();
if(stack.isEmpty()){
stack.push(i);
}
maxLen = Math.max(maxLen, i - stack.peek());
}
}
return maxLen;
}
}