From 8ac85d8a1f214a3abd02374d5a886c58f6d97351 Mon Sep 17 00:00:00 2001
From: Luke Else <mail@luke-else.co.uk>
Date: Thu, 14 Apr 2022 21:55:59 +0100
Subject: [PATCH] Added 'Delete' method to Binary Tree

---
 C#/Datastructures/BinaryTree/Tree.cs | 61 ++++++++++++++++++++++++++++
 C#/Program.cs                        |  4 +-
 2 files changed, 63 insertions(+), 2 deletions(-)

diff --git a/C#/Datastructures/BinaryTree/Tree.cs b/C#/Datastructures/BinaryTree/Tree.cs
index 0445254..13803a8 100644
--- a/C#/Datastructures/BinaryTree/Tree.cs
+++ b/C#/Datastructures/BinaryTree/Tree.cs
@@ -48,6 +48,67 @@ namespace C_.Datastructures.BinaryTree
             return;
         }
 
+        public bool Delete(T value)
+        {
+            //Check if root of tree is null
+            if (Count == 0)
+                return false;
+            
+            //Check if value is the root
+            if (Count == 1)
+            {
+                if (Root!.Value!.Equals(value))
+                {//If the only item is the one we are trying to delete
+                    Count = 0;
+                    Root = default;
+                    return true;
+                }
+                return false;
+            }
+
+            //Stack to store the items leading up to and including the one we are trying to delete    
+            Stack<TreeNode<T>>? deletionStack;
+
+            //Search for item being deleted + Parents
+            deletionStack = Find(value);
+
+            if (deletionStack == default)
+                return false; //Item was not found
+
+            //Delete Item (replace) and replace pointers to retain integrity of tree
+
+            TreeNode<T>? node = deletionStack.Pop();
+            TreeNode<T>? parent = deletionStack.Pop();
+
+            //stack to store the items leading up to the value that we will use to replace the node
+            Stack<TreeNode<T>>? replacementStack = Min(node!.Right);
+            if (replacementStack != default)
+            {//If there are values to the right
+                TreeNode<T>? replacementNode = replacementStack.Pop();
+
+                node.Value = replacementNode!.Value;
+
+                //Remove the node that we have taken the value from
+                if (replacementStack.Peek() != default)
+                {//If the parent is not the node that we replaced
+                    replacementStack.Pop()!.Left = replacementNode.Right;
+                }else{//If the parent is the node what we replaced
+                    node.Right = replacementNode.Right;
+                }
+            }else{
+                //Parent's relation needs to be set to null as there are no greater values
+                if (node.Value!.CompareTo(parent!.Value) < 0)
+                {//Item being deleted is the left child
+                    parent.Left = default;
+                }
+                //Item being deleted is the right value
+                parent.Right = default;
+            }
+            Count--;
+            return true;
+        }
+
+
         private Stack<TreeNode<T>>? Find(T value)
         {//Return true if the item can be found within the tree
             if (Root == default || Root.Value!.Equals(default))
diff --git a/C#/Program.cs b/C#/Program.cs
index 96bcf3b..82a9763 100644
--- a/C#/Program.cs
+++ b/C#/Program.cs
@@ -119,10 +119,10 @@ tree.Add(6);
 tree.Add(2);
 tree.Add(3);
 tree.Add(1);
-tree.Add(4);
+tree.Add(8);
 tree.Add(7);
 
-var x = tree.Find(2);
+var x = tree.Delete(4);
 
 Console.ReadLine();