二叉树相关算法

节点：

 class Node<T>
    {
        public T Value { get; set; }

        public Node<T> Left { get; set; }

        public Node<T> Right { get; set; }

        public Node(T value, Node<T> left, Node<T> right)
        {
            Value = value;
            Left = left;
            Right = right;
        }

        public Node(T value) : this(value, null, null) { }
    }

二叉树：

前中后深度优先遍历非递归，上到下（下到上）宽度优先遍历非递归，输出某层，获取深度

   class BinaryTree<T>
    {
        protected IComparer<T> comparer = Comparer<T>.Default; 

        public Node<T> Root { get; set; }

        public void Clear()
        {
            Root = null;
        }

        public void PreOrder()
        {
            if (Root == null)
                return;
            
            Stack<Node<T>> stack = new Stack<Node<T>>();
            stack.Push(Root);

            while (stack.Count > 0)
            {
                Node<T> node = stack.Pop();
                Console.Write(node.Value + " ");
                if (node.Right != null)
                    stack.Push(node.Right);
                if (node.Left != null)
                    stack.Push(node.Left);
            }         
        }

        public void MidOrder()
        {
            if (Root == null)
                return;

            Stack<Node<T>> stack = new Stack<Node<T>>();
            for (Node<T> current = Root; current != null || stack.Count > 0; current = current.Right)
            {
                while (current != null)
                {
                    stack.Push(current);
                    current = current.Left;
                }

                current = stack.Pop();
                Console.Write(current.Value + " ");
            }
        }

        public void AfterOrder()
        {
            if (Root == null)
                return;
            Stack<Node<T>> toVisit = new Stack<Node<T>>();
            Stack<bool> hasBeenProcessed = new Stack<bool>();
            Node<T> current = Root;
            if (current != null)
            {
                toVisit.Push(current);
                hasBeenProcessed.Push(false);
                current = current.Left;
            }

            while (toVisit.Count != 0)
            {
                if (current != null)
                {
                    toVisit.Push(current);
                    hasBeenProcessed.Push(false);
                    current = current.Left;
                }
                else
                {
                    bool processed = hasBeenProcessed.Pop();
                    Node<T> node = toVisit.Pop();
                    if (!processed)
                    {
                        toVisit.Push(node);
                        hasBeenProcessed.Push(true);  
                        current = node.Right;
                    }
                    else
                        Console.WriteLine(node.Value + " ");
                }
            }
        }

        public void UpDownOrder()
        {
            if (Root == null) 
                return;
            Queue<Node<T>> queue = new Queue<Node<T>>();
            queue.Enqueue(Root);
            
            while (queue.Count > 0)
            {
                Node<T> node = queue.Dequeue();
                Console.Write(node.Value + " ");
                if (node.Left != null)
                    queue.Enqueue(node.Left);
                if (node.Right != null)
                    queue.Enqueue(node.Right);
            }         
        }

        public void DownUpOrder()
        {
            if (Root == null)
                return;
            Queue<Node<T>> queue = new Queue<Node<T>>();
            queue.Enqueue(Root);
            Stack<Node<T>> stack = new Stack<Node<T>>();
            while (queue.Count > 0)
            {
                Node<T> node = queue.Dequeue();
                stack.Push(node);
                if (node.Left != null)
                    queue.Enqueue(node.Left);
                if (node.Right != null)
                    queue.Enqueue(node.Right);
            }
            int c = stack.Count;
            for (int i = 0; i < c; i++)
            {
                Console.Write(stack.Pop().Value + " ");
            }
        }

        public void PrintNodeAtLevel(int level)
        {
            if (level == 0) Console.Write(Root.Value + " ");
            PrintNodeAtLevel(Root, level);
        }

        private void PrintNodeAtLevel(Node<T> node, int level)
        {
            if (node == null || level < 0)
                return;
            if (level == 0)
            {
                Console.Write(node.Value + " ");
                return;
            }
            PrintNodeAtLevel(node.Left, level - 1);
            PrintNodeAtLevel(node.Right, level - 1);
        }

        public int GetDepth()
        {
            if (Root == null)
                return 0;
            return GetDepth(Root);
        }

        private int GetDepth(Node<T> node)
        {
            if (node == null) return 0;
            int l = GetDepth(node.Left);
            int r = GetDepth(node.Right);
            return Math.Max(l,r) + 1;
        }
    }

搜索二叉树：

搜索、包含、增加删除、获取父节点

 class BinarySearchTree<T> : BinaryTree<T>
    {
        public Node<T> Search(T data)
        {
            Node<T> current = Root;
            while (current != null)
            {
                int result = comparer.Compare(current.Value, data);
                if (result == 0)
                    return current;
                else if (result > 0)
                    current = current.Left;
                else if (result < 0)
                    current = current.Right;
            }
            return current;
        }

        public bool Contains(T data)
        {
            Node<T> current = Root;
            int result;
            while (current != null)
            {
                result = comparer.Compare(current.Value, data);
                if (result == 0)
                    return true;
                else if (result > 0)
                    current = current.Left;
                else if (result < 0)
                    current = current.Right;
            }
            return false;
        }

        public Node<T> GetParent(Node<T> node)
        {
            Node<T> current = base.Root, parent = null;
            while (current != null)
            {
                int result = comparer.Compare(current.Value, node.Value);
                if (result == 0)
                    return parent;
                else if (result > 0)
                {
                    parent = current;
                    current = current.Left;
                }
                else if (result < 0)
                {
                    parent = current;
                    current = current.Right;
                }
            }
            return parent;
        }

        public void Add(T data)
        {
            Node<T> n = new Node<T>(data);
            int result;

            Node<T> current = base.Root, parent = null;
            while (current != null)
            {
                result = comparer.Compare(current.Value, data);
                if (result == 0)
                    return;
                else if (result > 0)
                {
                    parent = current;
                    current = current.Left;
                }
                else if (result < 0)
                {
                    parent = current;
                    current = current.Right;
                }
            }

            if (parent == null)
                base.Root = n;
            else
            {
                result = comparer.Compare(parent.Value, data);
                if (result > 0)
                    parent.Left = n;
                else
                    parent.Right = n;
            }
        }

        public bool Remove(T data)
        {
            if (base.Root == null)
                return false;   

            Node<T> current = base.Root, parent = null;
            int result = comparer.Compare(current.Value, data);
            while (result != 0)
            {
                if (result > 0)
                {
                    parent = current;
                    current = current.Left;
                }
                else if (result < 0)
                {
                    parent = current;
                    current = current.Right;
                }

                if (current == null)
                    return false;
                else
                    result = comparer.Compare(current.Value, data);
            }

            if (current.Right == null)
            {
                if (parent == null)
                    base.Root = current.Left;
                else
                {
                    result = comparer.Compare(parent.Value, current.Value);
                    if (result > 0)
                        parent.Left = current.Left;
                    else if (result < 0)
                        parent.Right = current.Left;
                }
            }
            
            else if (current.Right.Left == null)
            {
                current.Right.Left = current.Left;

                if (parent == null)
                    base.Root = current.Right;
                else
                {
                    result = comparer.Compare(parent.Value, current.Value);
                    if (result > 0)
                        parent.Left = current.Right;
                    else if (result < 0)
                        parent.Right = current.Right;
                }
            }
            else
            {
                Node<T> leftmost = current.Right.Left, lmParent = current.Right;
                while (leftmost.Left != null)
                {
                    lmParent = leftmost;
                    leftmost = leftmost.Left;
                }

                lmParent.Left = leftmost.Right;

                leftmost.Left = current.Left;
                leftmost.Right = current.Right;

                if (parent == null)
                    base.Root = leftmost;
                else
                {
                    result = comparer.Compare(parent.Value, current.Value);
                    if (result > 0)
                        parent.Left = leftmost;
                    else if (result < 0)
                        parent.Right = leftmost;
                }
            }
            
            current.Left = current.Right = null;
            current = null;

            return true;
        }
    }