New tasks

6. Zigzag Conversion/6. Zigzag Conversion.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net7.0</TargetFramework>
+    <RootNamespace>_6._Zigzag_Conversion</RootNamespace>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

6. Zigzag Conversion/Program.cs

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+namespace _6._Zigzag_Conversion;
+
+internal class Program
+{
+    static void Main(string[] args)
+    {
+        Console.WriteLine(new Solution().Convert("PAYPALISHIRING", 3));
+    }
+}

6. Zigzag Conversion/Solution.cs

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+using System.Text;
+
+namespace _6._Zigzag_Conversion;
+
+public class Solution {
+    public string Convert(string s, int numRows)
+    {
+        if (numRows == 1)
+            return s;
+        int stepDown = (numRows-2) * 2 + (numRows>0 ? 1 : 0);
+        int stepTop = 0;
+        StringBuilder sb = new StringBuilder();
+        for (int start = 0; start < numRows; start++)
+        {
+            int j = start;
+            bool toDown = true;
+            while (j<s.Length)
+            {
+                sb.Append(s[j]);
+                if (stepDown == 0)
+                    j += stepTop;
+                else if (stepTop == 0)
+                    j += stepDown;
+                else if (toDown)
+                    j += stepDown;
+                else
+                    j += stepTop;
+                j++;
+                toDown = !toDown;
+            }
+            stepDown -= 2;
+            if (stepDown < 0)
+                stepDown = 0;
+            if (stepTop == 0)
+                stepTop = 1;
+            else
+                stepTop += 2;
+        }
+        return sb.ToString();
+    }
+}