四种常用的遍历二叉树的算法：

• DLR先序遍历
• LDR中序遍历
• LRD后序遍历
• 层次遍历

以下是简单的C++实现

#include <iostream>
#include <queue>

using namespace std;

typedef char ElemType;
typedef struct BNode {
    ElemType data;
    struct BNode *lchild, *rchild;
}BNode, *BTree;

void func(BTree &T) {
    cout << T->data << endl;
}

void createByNote(BTree &T) {
    char ch;
    cin >> ch;
    if (ch == '#')
        T = NULL;
    else {
        T = new BNode;
        T->data = ch;
        createByNote(T->lchild);
        createByNote(T->rchild);
    }
}

void preOrder(BTree T) {
    if (T) {
        func(T);
        preOrder(T->lchild);
        preOrder(T->rchild);
    }
}

void inOrder(BTree T) {
    if (T) {
        inOrder(T->lchild);
        func(T);
        inOrder(T->rchild);
    }
}

void posOrder(BTree T) {
    if (T) {
        posOrder(T->lchild);
        posOrder(T->rchild);
        func(T);
    }
}

void a(BTree T) {
    cout << "preOrder:" << endl;
    preOrder(T);
    cout << "inOrder:" << endl;
    inOrder(T);
    cout << "posOrder:" << endl;
    posOrder(T);
}

bool levelTraverse(BTree T) {
    if (!T) return false;

    BTree p;
    queue<BTree> Q;
    Q.push(T);

    while (!Q.empty()) {
        p = Q.front();
        Q.pop();
        func(T);
        if (p->lchild != NULL)
            Q.push(p->lchild);
        if (p->rchild != NULL)
            Q.push(p->rchild);
    }
    return true;
}

int main() {
    BTree T1;
    createByNote(T1);
    levelTraverse(T1);
    return 0;
}