c++ 先序构建二叉树

二叉树首先要解决构建问题，才能考虑后续的遍历，这里贴出通过先序构建二叉树，同时包含四种二叉树的遍历方法（先序，中序，后序，逐层）

第一、定义BinaryTreeNode 类

 #include <iostream>
 #include <string>
 #include <queue>
 using namespace std;

 template<typename T >class BinaryTree;
 template <typename T> class BinaryTreeNode {
 public:
     friend class BinaryTree<T>;
     BinaryTreeNode() {
         data = NULL;
         lChild = rChild = NULL;
     }
     BinaryTreeNode(T newdata) {
         this->data = newdata;
         lChild = rChild = NULL;
     }
     T getData() {
         return data;
     }
     BinaryTreeNode<T> * getLeftNode() {
         return lChild;
     }
     BinaryTreeNode<T> * getRightNode() {
         return rChild;
     }
     T data;
     BinaryTreeNode<T>* lChild;
     BinaryTreeNode<T>* rChild;
 private:

 };

第二、定义BinaryTree 类

 template <typename T> class BinaryTree {
 public:
     BinaryTreeNode<T> *root;
     char* p;
     BinaryTree() { root = NULL; }
     BinaryTree(T data) {
         root = new BinaryTreeNode<T>(data);
         root->lChild = NULL;
         root->rChild = NULL;
     }
     ~BinaryTree() {
         delete root;
     }

     //构建二叉树并返回
     BinaryTreeNode<T>* CreateTree() {
         BinaryTreeNode<int>* bt = NULL;
         char t;
         cin >> t;
         if (t == '#')
         {
             return NULL;
         }
         else {
             int num = t - '';
             bt = new BinaryTreeNode<T>(num);
             bt->lChild = CreateTree();
             bt->rChild = CreateTree();
         }
         return bt;
     }

     //先序构建二叉树
     BinaryTreeNode<T>* PreCreateTree() {
         BinaryTreeNode<int>* bt = NULL;
         if (this->root == NULL)
         {
             cout << "请输入根节点（#代表空树）:";
         }
         else {
             cout << "请输入节点（#代表空树）:";
         }
         char t;
         cin >> t;
         if (t == '#')
         {
             return NULL;
         }
         else {
             int num = t - '';
             bt = new BinaryTreeNode<T>(num);
             if (this->root == NULL)
             {
                 this->root = bt;
             }
             cout << bt->data << "的左孩子";
             bt->lChild = PreCreateTree();

             cout << bt->data << "的右边孩子";
             bt->rChild = PreCreateTree();
         }
         return bt;
     }   

     void preOderTraversal(BinaryTreeNode<T> *bt);  //先序遍历
     void inOrderTraversal(BinaryTreeNode<T> *bt);  //中序遍历
     void postOrderTraversal(BinaryTreeNode<T> *bt);//后序遍历
     void levelTraversal(BinaryTreeNode<T> *bt);    //逐层遍历

 private:

 };

 template <typename T>
 void BinaryTree<T>::preOderTraversal(BinaryTreeNode<T> *bt) {
     if (bt)
     {
         cout << bt->data;
         BinaryTree<T>::preOderTraversal(bt->getLeftNode());
         BinaryTree<T>::preOderTraversal(bt->getRightNode());
     }
 }

 template <typename T>
 void BinaryTree<T>::inOrderTraversal(BinaryTreeNode<T> *bt) {
     if (bt)
     {
         BinaryTree<T>::inOrderTraversal(bt->getLeftNode());
         cout << bt->data;
         BinaryTree<T>::inOrderTraversal(bt->getRightNode());
     }
 }

 template <typename T>
 void BinaryTree<T>::postOrderTraversal(BinaryTreeNode<T> *bt) {
     if (bt)
     {
         BinaryTree<T>::postOrderTraversal(bt->getLeftNode());
         BinaryTree<T>::postOrderTraversal(bt->getRightNode());
         cout << bt->data;
     }
 }

 template <typename T>
 void BinaryTree<T>::levelTraversal(BinaryTreeNode<T> *bt) {

     queue<BinaryTreeNode<T>*> que;
     que.push(bt);
     while (!que.empty())
     {
         BinaryTreeNode<T>* proot = que.front();
         que.pop();
         cout << proot->data;

         if (proot->lChild != NULL)
         {
             que.push(proot->lChild);//左孩子入队
         }
         if (proot->rChild != NULL)
         {
             que.push(proot->rChild);//右孩子入队
         }
     }
 }

第三、主程序运行

 #include "pch.h"
 #include <iostream>
 #include "BinaryTree.h"

 int main()
 {
     //场景测试2
     BinaryTree<int> btree;
     btree.PreCreateTree();//先序构建二叉树
     cout << "先序遍历:";
     btree.preOderTraversal(btree.root); cout << endl;//先序遍历
     cout << "中序遍历:";
     btree.inOrderTraversal(btree.root); cout << endl;//中序遍历
     cout << "后序遍历:";
     btree.postOrderTraversal(btree.root); cout << endl;//后序遍历
     cout << "逐层序遍历:";
     btree.levelTraversal(btree.root);

 }

最终测试运行截图