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LongestValidParenthesis.java
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LongestValidParenthesis.java
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package Leetcode;
import java.util.ArrayDeque;
import java.util.Deque;
/**
* @author kalpak
*
* 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 ')'.
*/
public class LongestValidParenthesis {
public static int longestValidParentheses(String s) {
int result = 0;
Deque<Integer> stack = new ArrayDeque<>();
// You can imagine there is a ) at index -1 position
// i.e. s[-1] = ')'
stack.push(-1);
for(int i = 0; i < s.length(); i++) {
if(s.charAt(i) == '(')
stack.push(i);
else {
// if there is a match (i.e. "()"), then we can pop the stack
// and update the max length by (i - indices.top())
// (because the string in (indices.top(), i] is a valid parenthese)
// else if there isn't a match (i.e. "))"), then we can substitute
// the top of the stack by the latest one
stack.pop();
if(stack.isEmpty())
stack.push(i); // if the stack is empty, it means a "))" occurs
else
result = Math.max(result, i - stack.peek()); // "()" occurs
}
}
return result;
}
public static void main(String[] args) {
String str = ")()())";
System.out.println(longestValidParentheses(str));
}
}