求c++或c由先序中序遍历得出并打印树形二叉树，如下图。

Question

如图 15
/ \
12 23
/ \
9 25求给出代码！！！！

Answer 1

如果是单纯的遍历，只需要输出数字即可，代码如下

#include <iostream>
using namespace std;

template <typename T>
struct binaryTreeNode
{
    T element;
    binaryTreeNode<T> *leftChild, *rightChild;

    binaryTreeNode() {
        leftChild = rightChild = NULL;
    }

    binaryTreeNode(const T &theElement) : element(theElement)
    {
        leftChild = rightChild = NULL;
    }

    binaryTreeNode(const T &theElement, binaryTreeNode *theLeftChild, binaryTreeNode *theRightChild) : element(theElement)
    {
        leftChild = theLeftChild;
        rightChild = theRightChild;
    }
};

template <typename T>
void printvalue(binaryTreeNode<T> *t)
{
    cout << t->element << ' ';
}

template <typename T>
void preOrder(binaryTreeNode<T> *t) 
{
    if(t != NULL)
    {
        printvalue(t);                      // 输出元素
        preOrder(t->leftChild);     // 前序遍历左子树
        preOrder(t->rightChild);        // 后序遍历右子树
    }
}

template <typename T>
void inOrder(binaryTreeNode<T> *t)
{
    if(t != NULL)
    {
        inOrder(t->leftChild);        // 中序遍历左子树
        printvalue(t);                      // 输出元素
        inOrder(t->rightChild);         // 中序遍历右子树
    }
}

int main()
{
    binaryTreeNode<int> *first, *second, *third, *four, *five, *six, *seven;
    seven = new binaryTreeNode<int>(7);
    six = new binaryTreeNode<int>(6);
    five = new binaryTreeNode<int>(25);
    four = new binaryTreeNode<int>(9);
    third = new binaryTreeNode<int>(23, six, seven);
    second = new binaryTreeNode<int>(12, four, five);
    first = new binaryTreeNode<int>(15, second, third);
    cout << "先序遍历：";
    preOrder(first);
    cout << endl;
    cout << "中序遍历：";
    inOrder(first);
    // PrintNodeByLevel(first);
    return 0;
}

博客里用这些代码和部分解析

如果要输出有树形的二叉树，代码如下

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

template <typename T>
struct binaryTreeNode
{
    T element;
    binaryTreeNode<T> *leftChild, *rightChild;

    binaryTreeNode() {
        leftChild = rightChild = NULL;
    }

    binaryTreeNode(const T &theElement) : element(theElement)
    {
        leftChild = rightChild = NULL;
    }

    binaryTreeNode(const T &theElement, binaryTreeNode *theLeftChild, binaryTreeNode *theRightChild) : element(theElement)
    {
        leftChild = theLeftChild;
        rightChild = theRightChild;
    }
};

template <typename T>
void printvalue(binaryTreeNode<T> *t)
{
    cout << t->element << ' ';
}

template <typename T>
void PrintNodeByLevel(binaryTreeNode<T>* root) {
    queue<binaryTreeNode<T>*> Q;
    queue<string> C; 
    Q.push(root);
    Q.push(0);
    do {
        binaryTreeNode<T>* node = Q.front();
        Q.pop();
        if (node) {
            cout << node->element << " ";
            if (node->leftChild) {
                Q.push(node->leftChild);
                C.push("/");
            }
            if (node->rightChild) {
                Q.push(node->rightChild);
                C.push("\\");
            }
        }
        else if (!Q.empty()) {
            cout << endl;
            while(C.size() != 0) {
                cout << C.front() << " ";
                C.pop();
            }
            Q.push(0);
            cout << endl;
        }
    } while (!Q.empty());
}

int main()
{
    binaryTreeNode<int> *first, *second, *third, *four, *five, *six, *seven;
    seven = new binaryTreeNode<int>(7);
    six = new binaryTreeNode<int>(6);
    five = new binaryTreeNode<int>(25);
    four = new binaryTreeNode<int>(9);
    third = new binaryTreeNode<int>(23, six, seven);
    second = new binaryTreeNode<int>(12, four, five);
    first = new binaryTreeNode<int>(15, second, third);
    PrintNodeByLevel(first);
    return 0;
}