32. Longest Valid Parentheses

32. Longest Valid Parentheses/32. Longest Valid Parentheses.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net10.0</TargetFramework>
+    <RootNamespace>_32._Longest_Valid_Parentheses</RootNamespace>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

32. Longest Valid Parentheses/Program.cs

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+var sol = new Solution();
+
+// System.Console.WriteLine(sol.LongestValidParentheses(")()())"));
+// System.Console.WriteLine(sol.LongestValidParentheses("()(()"));
+System.Console.WriteLine(sol.LongestValidParentheses("()(())"));

32. Longest Valid Parentheses/Solution.cs

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+public class Solution
+{
+    struct Item
+    {
+        public char Sym;
+        public int Count;
+        public char? PrevSym;
+    }
+
+    public int LongestValidParentheses(string s)
+    {
+        var stack = new Stack<Item>();
+        var answer = 0;
+        foreach (var ch in s)
+        {
+            if (stack.Count > 0 && (stack.Peek().Sym == '(' || stack.Peek().PrevSym == '(') && ch == ')')
+            {
+                var prev = stack.Pop();
+                var count = 2;
+                if (prev.Sym == '#')
+                {
+                    stack.Pop();
+                    count += prev.Count;
+                }
+                while (stack.Count > 0 && stack.Peek().Sym == '#')
+                    count += stack.Pop().Count;
+                char? prevSym = null;
+                if (stack.Count > 0)
+                    prevSym = stack.Peek().Sym;
+                stack.Push(new Item() { Sym = '#', Count = count, PrevSym = prevSym });
+                answer = Math.Max(answer, count);
+            }
+            else
+            {
+                stack.Push(new Item() { Sym = ch, Count = 0 });
+
+
+            }
+        }
+
+        return answer;
+    }
+}