From b2de726a4fdb1d7f44080f42690bec9a4adbb137 Mon Sep 17 00:00:00 2001
From: JeffLiu <Jeffliuapple@gmail.com>
Date: Sat, 18 Jul 2020 23:05:51 +0800
Subject: [PATCH] [Stack] Add a solution to Longest Valid Parentheses

---
 Stack/LongestValidParentheses.swift | 43 +++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/Stack/LongestValidParentheses.swift b/Stack/LongestValidParentheses.swift
index 0c74b1f8..6e6a0c87 100644
--- a/Stack/LongestValidParentheses.swift
+++ b/Stack/LongestValidParentheses.swift
@@ -29,3 +29,46 @@ class LongestValidParentheses {
         return longest
     }
 }
+
+
+class LongestValidParenthesesWithoutExtraSpace {
+    func longestValidParentheses(_ s: String) -> Int {
+        var longest = 0, leftCount = 0, rightCount = 0
+        
+        for char in s {
+            if char == "(" {
+                leftCount += 1
+            } else {
+                rightCount += 1
+            }
+            
+            if leftCount == rightCount {
+                longest = max(longest, leftCount + rightCount)
+            } else if leftCount < rightCount {
+                leftCount = 0
+                rightCount = 0
+            }
+        }
+        
+        leftCount = 0
+        rightCount = 0
+        
+        for char in s.reversed() {
+            if char == "(" {
+                leftCount += 1
+            } else {
+                rightCount += 1
+            }
+            
+            if leftCount == rightCount {
+                longest = max(longest, leftCount + rightCount)
+            } else if leftCount > rightCount {
+                leftCount = 0
+                rightCount = 0
+            }
+        }
+        
+        return longest
+    }
+}
+