算法学习二叉查找树

     创建二叉查找树、查找二叉树中的某个节点、删除某个节点、

     新增节点、查找某个节点的父节点、查找最小节点

     对二叉树进行前序遍历、中序遍历、后序遍历

     前序遍历，也叫先根遍历，遍历的顺序是，根，左子树，右子树 　
     中序遍历，也叫中根遍历，顺序是 左子树，根，右子树

　   后序遍历，也叫后根遍历，遍历顺序，左子树，右子树，根

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace SuanFa
{
    public  class Order
    {
        //创建二分查找树
        public  Tree  CreateBinaryTree(int[] A)
        {
            if (A == null || A.Length == 0)
            {
                return null;
            }
            
            Tree root = new Tree(A[0]); //根节点 相当于表头指针          
            Tree treeNode,temp;//要添加的节点和中间节点
            
            for (int i = 1; i < A.Length; i++)
            {
                temp = root;
                treeNode = new Tree(A[i]);
                AddTreeNode(temp, treeNode);
            }

            return root;
        }

        //添加树节点
        private void AddTreeNode(Tree tree, Tree node)
        {
            if (node.Text < tree.Text)//添加左子节点
            {
                if (tree.LeftTree.Count == 0)
                {
                    tree.LeftTree.Add(node);
                }
                else {
                    AddTreeNode(tree.LeftTree[0], node);
                }                
            }
            else if (node.Text > tree.Text)//添加右子节点
            {
                if (tree.RightTree.Count == 0)
                {
                    tree.RightTree.Add(node);
                }
                else
                {
                    AddTreeNode(tree.RightTree[0], node);
                }   
            }
        }

        //查找某个节点
        public Tree Find(Tree root,int text) {
            if (root == null)//如果当前节点为null 返回null
            {
                return null;
            }

            if (root.Text == text)//如果等于当前节点就返回当前节点
            {
                return root;
            }

            if (root.LeftTree.Count > 0)//递归左子树
            {
                if (root.Text > text)
                {
                    return Find(root.LeftTree[0],text);
                }
            }

            if (root.RightTree.Count > 0)//递归右子树
            {
                if (root.Text<text)
                {
                    return Find(root.LeftTree[0], text);
                }
            }

            return null;//没找到返回null
        }

        //查找某个节点的父节点
        public Tree FindF(Tree root, int text)
        {
            if (root == null)//如果当前节点为null 返回null
            {
                return null;
            }

            if (root.LeftTree.Count > 0)
            {
                if (root.LeftTree[0].Text == text)//如果等于当前节点的左子节点就返回当前节点
                {
                    return root;
                }
                if (root.Text > text)//递归左子树
                {
                    return FindF(root.LeftTree[0], text);
                }
            }

            if (root.RightTree.Count > 0)
            {
                if (root.RightTree[0].Text == text)//如果等于当前节点的右子节点就返回当前节点
                {
                    return root;
                }
                if (root.Text < text)//递归右子树
                {
                    return FindF(root.RightTree[0], text);
                }
              
            }
             
            return null;//没找到返回null
        }

        //前序遍历
        public int DLR(Tree tree,List<int> list)
        {
            if (tree == null || list == null)
            {
                return 0;
            }

            list.Add(tree.Text);  //根节点

            if (tree.LeftTree.Count > 0)   //先遍历左子树
            {
                 DLR(tree.LeftTree[0],list);
            }
             
            if (tree.RightTree.Count > 0)  //右子树
            {
                DLR(tree.RightTree[0], list);
            }

            if (list.Count > 0)
                return 1;
            return 0;
        }

        //后序遍历
        public int LRD(Tree tree, List<int> list)
        {
            if (tree == null || list == null)
            {
                return 0;
            }


            if (tree.LeftTree.Count > 0)   //先遍历左子树
            {
                LRD(tree.LeftTree[0], list);
            }

            if (tree.RightTree.Count > 0)  //右子树
            {
                LRD(tree.RightTree[0], list);
            }

            list.Add(tree.Text);  //根节点
             
            if (list.Count > 0)
                return 1;
            return 0;
        }

        //中序遍历
        public int LDR(Tree tree, List<int> list)
        {
            if (tree == null || list == null)
            {
                return 0;
            }
             
            if (tree.LeftTree.Count > 0)   //先遍历左子树
            {
                LDR(tree.LeftTree[0], list);
            }

            list.Add(tree.Text);  //根节点

            if (tree.RightTree.Count > 0)  //右子树
            {
                LDR(tree.RightTree[0], list);
            }

            if (list.Count > 0)
                return 1;
            return 0;
        }

        //删除节点
        //1：节点不存在 
        //2：节点存在且没有子树 
        //3：节点存在且有左子树，用以要删除节点为根节点树的最小节点代替当前节点
        //4；节点存在且只有右子树，用药删除节点的右子节点代替当前节点
        public Tree Delete(Tree tree, int text)
        {
            if (tree == null)
            {
                return null;
            }
            Tree newTree = tree;
            //要删除节点的父节点
            Tree delFNode = FindF(newTree, text);

            //要删除的节点
            Tree delNode;
            bool isleft = true;//标识被删节点是其所在树的左子节点还是右子节点

            if (delFNode == null)//要删除的节点父节点为空有两种情况。1不存在；2是根节点
            {
                delNode = Find(newTree, text);
                if (delNode == null)//不存在
                {
                    return newTree;
                }
                Tree tmp;
                if (delNode.LeftTree.Count > 0)//存在左子树
                {
                    tmp = FindMin(delNode);
                    Tree tmpF = FindF(delNode, tmp.Text);
                    tmpF.LeftTree.Remove(tmp);
                    tmp.LeftTree.Add(delNode.LeftTree[0]);
                    if (delNode.RightTree.Count > 0)
                    {
                        tmp.RightTree.Add(delNode.RightTree[0]);
                    }
                    newTree = tmp;
                }
                else if (delNode.RightTree.Count > 0)//只有右子树
                {
                    newTree = delNode.RightTree[0];
                }

                return newTree;

            }//要删除的节点是左子树
            else if (delFNode.LeftTree.Count > 0 && delFNode.LeftTree[0].Text == text)
            {
                delNode = delFNode.LeftTree[0];
                isleft = true;
            }//要删除的节点是右子树
            else if (delFNode.RightTree.Count > 0 && delFNode.RightTree[0].Text == text)
            {
                delNode = delFNode.RightTree[0];
                isleft = false;
            }
            else//要删除的节点不存在
            {
                return newTree;
            }

            Tree temp;
            //如果存在左子树，就用左子树的最小节点取代要删除的节点，并删除这个最小节点
            if (delNode.LeftTree.Count > 0)
            {
                temp = FindMin(delNode);

                Tree tempDelNode = delNode;
                while (tempDelNode.LeftTree.Count > 0)
                {
                    tempDelNode = tempDelNode.LeftTree[0];
                }
                if (temp.Text != delNode.LeftTree[0].Text)
                {
                    temp.LeftTree.Add(delNode.LeftTree[0]);
                }
                delNode.LeftTree.Remove(tempDelNode);
                 
                //把要删除节点的右子树作为最小节点的右子树
                if (delNode.RightTree.Count > 0)
                {
                    temp.RightTree.Add(delNode.RightTree[0]);
                }

                if (isleft)
                {
                    delFNode.LeftTree.Add(temp);
                    delFNode.LeftTree.Remove(delNode);
                }
                else
                {
                    delFNode.RightTree.Add(temp);
                    delFNode.RightTree.Remove(delNode);
                }
            }
            else if (delNode.RightTree.Count > 0)
            {
                delFNode.RightTree.Add(delNode.RightTree[0]);
            }

            return newTree;
        }

        //查找最小节点
        public Tree FindMin(Tree tree)
        {
            if (tree == null)
            {
                return null;
            }

            //如果当前节点没有左子树就返回他自己
            if (tree.LeftTree.Count == 0)
            {
                return tree;
            }

            //递归左子树
          return  FindMin(tree.LeftTree[0]);
 
        }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace SuanFa
{
  public  class Tree
    {
      //显示的值
      public int Text
      {
          set;
          get;
      }

      //构造函数
      public Tree(int text) {
          this.Text = text;
          if (LeftTree == null)
          {
              LeftTree = new List<Tree>();
          }
          if (RightTree == null)
          {
              RightTree = new List<Tree>();
          }
      }

      //左子树
      public List<Tree> LeftTree
      {
          set;
          get;
      }

      //右子树
      public List<Tree> RightTree
      {
          set;
          get;
      }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace SuanFa
{
    class Program
    {
        static void Main(string[] args)
        {           
            int[] B = new int[] { 50,25,75,15,35,65,85,10,20,30,40,60,70,80,90 };         
            Order order = new Order();
            Tree tree= order.CreateBinaryTree(B);
          
            Console.Write("原先数组：");
            foreach (int i in B)
            {
                Console.Write(i.ToString() + "  ");
            }
            Console.WriteLine();
            Console.Write("----------------------------形成二叉查找树--------------------------");
            Console.WriteLine();
            Console.WriteLine("删除前:");
            Console.WriteLine();
            Show(B, order, tree);
            Console.WriteLine();
            Console.WriteLine();
            Tree newTree = order.Delete(tree,50);
            Console.WriteLine("删除跟节点50后:");
            Console.WriteLine();
            Show(B, order, newTree);
            Console.WriteLine();
            Console.WriteLine();
            Tree newTree1 = order.Delete(newTree, 65);
            Console.WriteLine("删除65后:");
            Console.WriteLine();
            Show(B, order, newTree1);
            Console.ReadLine();
        }

        private static void Show(int[] B, Order order, Tree tree)
        {                    
            List<int> listDlr = new List<int>();
            if (order.DLR(tree, listDlr) > 0)
            {
                Console.Write("前序遍历：");
                foreach (int i in listDlr)
                {
                    Console.Write(i.ToString() + "  ");
                }
                Console.WriteLine();
                Console.WriteLine();
            }

            List<int> listLrd = new List<int>();
            if (order.LRD(tree, listLrd) > 0)
            {
                Console.Write("后序遍历：");
                foreach (int i in listLrd)
                {
                    Console.Write(i.ToString() + "  ");
                }
                Console.WriteLine();
                Console.WriteLine();
            }

            List<int> listLdr = new List<int>();
            if (order.LDR(tree, listLdr) > 0)
            {
                Console.Write("中序遍历：");
                foreach (int i in listLdr)
                {
                    Console.Write(i.ToString() + "  ");
                }
            }
        }
    }
}