Longest Valid Parentheses
Given a string containing just the characters '(' and ')', find the length of the longest valid (well-formed) parentheses substring.
For "(()", the longest valid parentheses substring is "()", which has length = 2.
Another example is ")()())", where the longest valid parentheses substring is "()()", which has length = 4.
public class Solution {
public int longestValidParentheses(String s) {
if (s == null || s.length() == 0) {
return 0;
}
Stack<Integer> stack = new Stack<>();
int start = 0, maxLen = 0;
for (int i = 0; i < s.length(); i++) {
if (s.charAt(i) == '(') {
stack.push(i);
} else {
if (stack.isEmpty()) {
start = i + 1;
} else {
stack.pop();
if (stack.isEmpty()) {
maxLen = Math.max(maxLen, i - start + 1);
} else {
maxLen = Math.max(maxLen, i - stack.peek());
}
}
}
}
return maxLen;
}
}
Hope this helps,
Michael