added LongestValidParentheses solution

Author: Iurii-Dziuban

README.md

@@ -120,6 +120,7 @@ The platform currently supports a total of 11 languages: C, C++, Java, Python, C
 - 19 RemoveNthNodeFromEndOfList (RemoveNthNodeFromEndOfListTest) - linked list remove
 - 20 ValidParentheses same as BalancedParentheses (BalancedParenthesesTest)
 - 22 GenerateParentheses (GenerateParenthesesTest) - generate all valid combinations of n parentheses
+- 32 LongestValidParentheses (LongestValidParenthesesTest) - find longest substring of valid parentheses
 - 42 TrappingRainWater (TrappingRainWaterTest) - calculate water inside the landscape
 - 44 WildcardMatching (WildcardMatchingTest) - checking wildcard pattern matching
 - 45 JumpGame2 (JumpGame2Test) - Jump Game / Tower Hopper problem / Minimum number of jumps to reach the high based on possible range to jump from current element.

src/main/java/iurii/job/interview/leetcode/LongestValidParentheses.java

@@ -0,0 +1,44 @@
+package iurii.job.interview.leetcode;
+
+/**
+ * 32. Longest Valid Parentheses https://leetcode.com/problems/longest-valid-parentheses/description/
+ *
+ * Ideas are here https://leetcode.com/articles/longest-valid-parentheses/
+ *
+ * Brute force, dynamic programming, stack and two pointers
+ *
+ * Time complexity: O(N)
+ * Auxiliary space complexity: O(N) with stack and O(1) with two pointers
+ */
+public class LongestValidParentheses {
+
+    public int longestValidParentheses(String s) {
+        int left = 0, right = 0, maxLength = 0;
+        for (int i = 0; i < s.length(); i++) {
+            if (s.charAt(i) == '(') {
+                left++;
+            } else {
+                right++;
+            }
+            if (left == right) {
+                maxLength = Math.max(maxLength, left + right);
+            } else if (right > left) {
+                left = right = 0;
+            }
+        }
+        left = right = 0;
+        for (int i = s.length() - 1; i >= 0; i--) {
+            if (s.charAt(i) == '(') {
+                left++;
+            } else {
+                right++;
+            }
+            if (left == right) {
+                maxLength = Math.max(maxLength, left + right);
+            } else if (left > right) {
+                left = right = 0;
+            }
+        }
+        return maxLength;
+    }
+}

src/test/java/iurii/job/interview/leetcode/LongestValidParenthesesTest.java

@@ -0,0 +1,15 @@
+package iurii.job.interview.leetcode;
+
+import org.junit.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class LongestValidParenthesesTest {
+    @Test
+    public void test() {
+        LongestValidParentheses longestValidParentheses = new LongestValidParentheses();
+        assertThat(longestValidParentheses.longestValidParentheses(")()())")).isEqualTo(4);
+        assertThat(longestValidParentheses.longestValidParentheses("()")).isEqualTo(2);
+        assertThat(longestValidParentheses.longestValidParentheses(")))(((")).isEqualTo(0);
+    }
+}