从上往下打印出二叉树的每个结点，同一层按照从左到右的顺序打印

#include
#include
using namespace std;

struct BinaryTreeNode
{
int data;
struct BinaryTreeNode *lchild;
struct BinaryTreeNode *rchild;
};

typedef struct BinaryTreeNode BinTreeNode;

//先序构造二叉树
BinTreeNode* preOrderCreateTree(BinTreeNode *head)
{
int tmp;
cin >> tmp;
if (tmp == 0)
head = NULL;
else
{
head = new BinTreeNode;
head->data = tmp;
head->lchild = preOrderCreateTree(head->lchild);
head->rchild = preOrderCreateTree(head->rchild);
}

return head;
}

//先序遍历二叉树
void preVisitTree(const BinTreeNode *head)
{
if (head == NULL)
return;

cout << head->data;
preVisitTree(head->lchild);
preVisitTree(head->rchild);
}

void freeTree(BinTreeNode *head)
{
if (head == NULL)
return;

freeTree(head->lchild);
freeTree(head->rchild);
delete head;
}

void printOrderByLayer(const BinTreeNode *head)
{
if (head == NULL)
return;

deque myDeque;
myDeque.push_back(head);
while (myDeque.size() > 0)
{
const BinTreeNode *tmp = myDeque.front();
myDeque.pop_front();
cout << tmp->data;
if (tmp->lchild)
myDeque.push_back(tmp->lchild);
if (tmp->rchild)
myDeque.push_back(tmp->rchild);
}
}

int main()
{
BinTreeNode *root = preOrderCreateTree(root);
preVisitTree(root);
cout << endl;
printOrderByLayer(root);
cout << endl;
freeTree(root);
return 0;
}