https://leetcode.com/problems/binary-tree-zigzag-level-order-traversal/

Author: harshitgindra

LeetCodeSolutions/BinaryTreeBfs/BinaryTreeZigzagLevelOrderTraversal.cs

@@ -0,0 +1,67 @@
+namespace LeetCodeSolutions.BinaryTreeBfs
+{
+    class BinaryTreeZigzagLevelOrderTraversal
+    {
+        public IList<IList<int>> ZigzagLevelOrder(TreeNode root)
+        {
+            // Create a dictionary to store nodes at each level
+            var levelMap = new Dictionary<int, IList<int>>();
+
+            // Perform a depth-first traversal to populate the level map
+            TraverseBinaryTree(root, 0, levelMap);
+
+            // Convert the dictionary values to a list and return
+            return levelMap.Values.ToList();
+        }
+
+        private void TraverseBinaryTree(TreeNode node, int level, IDictionary<int, IList<int>> levelMap)
+        {
+            if (node == null) return;
+
+            // If this level hasn't been encountered before, add it to the dictionary
+            if (!levelMap.ContainsKey(level))
+            {
+                levelMap[level] = new List<int>();
+            }
+
+            // Add the node's value to the appropriate level
+            // For even levels, add to the end; for odd levels, add to the beginning
+            if (level % 2 == 0)
+            {
+                levelMap[level].Add(node.val);
+            }
+            else
+            {
+                levelMap[level].Insert(0, node.val);
+            }
+
+            // Recursively traverse left and right children
+            TraverseBinaryTree(node.left, level + 1, levelMap);
+            TraverseBinaryTree(node.right, level + 1, levelMap);
+        }
+
+        [Test(Description = "https://leetcode.com/problems/binary-tree-zigzag-level-order-traversal/")]
+        [Category("Medium")]
+        [Category("LeetCode")]
+        [Category("Binary Tree Zig Zag Level Order Traversal")]
+        [TestCaseSource(nameof(Input))]
+        [Category("Binary Tree BFS")]
+        [Category("TopInterview")]
+        public void Test1((IList<IList<int>> Output, int?[] Input) item)
+        {
+            var response = this.ZigzagLevelOrder(item.Input.ToTreeNode());
+            Assert.That(response, Is.EqualTo(item.Output));
+        }
+
+        public static IEnumerable<(IList<IList<int>> Output, int?[] Input)> Input =>
+            new List<(IList<IList<int>> Output, int?[] Input)>()
+            {
+                (new List<IList<int>>()
+                {
+                    new List<int>() { 3 },
+                    new List<int>() { 20, 9 },
+                    new List<int>() { 15, 7 },
+                }, [3, 9, 20, null, null, 15, 7])
+            };
+    }
+}