Merge pull request #1667 from bradhanson/csharp-0094-binary-tree-inorder-traversal-bh

Create 0094-binary-tree-inorder-traversal.cs

Author: Ahmad-A0

csharp/0094-binary-tree-inorder-traversal.cs

@@ -0,0 +1,48 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     public int val;
+ *     public TreeNode left;
+ *     public TreeNode right;
+ *     public TreeNode(int val=0, TreeNode left=null, TreeNode right=null) {
+ *         this.val = val;
+ *         this.left = left;
+ *         this.right = right;
+ *     }
+ * }
+ */
+public class Solution {
+    public IList<int> InorderTraversal(TreeNode root) {
+        // return InorderTraversalRecursive(root).ToList();
+        return InorderTraversalIterative(root).ToList();
+    }
+
+    // Time: O(n)
+    // Space: O(n)
+    private IEnumerable<int> InorderTraversalRecursive(TreeNode node) {
+        if (node == null) {
+            return Enumerable.Empty<int>();
+        }
+
+        return InorderTraversalRecursive(node.left)
+            .Append(node.val)
+            .Concat(InorderTraversalRecursive(node.right));
+    }
+
+    // Time: O(n)
+    // Space: O(n)
+    private IEnumerable<int> InorderTraversalIterative(TreeNode node) {
+        List<int> result = new();
+        Stack<TreeNode> stack = new();
+        while (node != null || stack.Any()) {
+            while (node != null) {
+                stack.Push(node);
+                node = node.left;
+            }
+            node = stack.Pop();
+            result.Add(node.val);
+            node = node.right;
+        }
+        return result;
+    }
+}