Add symmetric tree check and zigzag traversal method

Implemented the `IsSymmetric` and `IsMirror` methods in `101.SymmetricTree.cs` to check for symmetry in binary trees. Removed unnecessary using directive in `102.BinaryTreeLevelOrderTraversal.cs`. Introduced `103.BinaryTreeZigzagLevelOrderTraversal.cs` with a new `ZigzagLevelOrder` method for zigzag level order traversal of binary trees.

Author: ewdlop

101-110/101.Symmetric Tree.cs renamed to 101-110/101.SymmetricTree.cs

@@ -1,11 +1,4 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
-
-
-namespace LeetCodeNote;
+namespace LeetCodeNote;
 
 public static partial class Solution
 {
@@ -33,6 +26,4 @@ public static bool IsMirror(TreeNode root1, TreeNode root2)
         return (left && right);
 
     }
-}
-
- ? true : false;
+}

101-110/102.BinaryTreeLevelOrderTraversal.cs

@@ -3,7 +3,7 @@
 using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
-using static LeetCodeNote.Solution;
+namespace LeetCodeNote;
 
 public static partial class Solution
 {

101-110/103.BinaryTreeZigzagLevelOrderTraversal.cs

@@ -0,0 +1,72 @@
+using System.Collections.Generic;
+
+namespace LeetCodeNote;
+
+public static partial class Solution
+{
+    public static IList<IList<int>> ZigzagLevelOrder(TreeNode root)
+    {
+        IList<IList<int>> result = new List<IList<int>>();
+        if (root == null) return result;
+        Stack<TreeNode> stack = new Stack<TreeNode>();
+        stack.Push(root);
+        int level = 0;
+
+        while (stack.Count > 0)
+        {
+            IList<int> currLevel = new List<int>();
+            Queue<TreeNode> q = new Queue<TreeNode>();
+
+            while (stack.Count > 0)
+            {
+                q.Enqueue(stack.Pop());
+            }
+
+            if (level % 2 == 0)
+            {
+
+                while (q.Count > 0)
+                {
+                    TreeNode temp = q.Dequeue();
+
+                    if (temp.left != null)
+                    {
+                        stack.Push(temp.left);
+                    }
+
+                    if (temp.right != null)
+                    {
+                        stack.Push(temp.right);
+                    }
+
+                    currLevel.Add(temp.val);
+                }
+            }
+            else
+            {
+
+                while (q.Count > 0)
+                {
+                    TreeNode temp = q.Dequeue();
+
+                    if (temp.right != null)
+                    {
+                        stack.Push(temp.right);
+                    }
+
+                    if (temp.left != null)
+                    {
+                        stack.Push(temp.left);
+                    }
+
+                    currLevel.Add(temp.val);
+                }
+            }
+
+            result.Add(currLevel);
+            level++;
+        }
+
+        return result;
+    }
+}