從上往下打印出二叉樹的每個結點，同一層的結點按照從左到右的順序列印。

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

struct Node{  
	int   m_nData;  
	Node *m_pLeft;  
	Node *m_pRight;  
}; 

void traverseBinaryTreeByLevel(Node *pRoot)
{
	if (pRoot==NULL){
		return;
	}

	Node *pNode = NULL;
	deque<Node*> q;
	q.push_back(pRoot);

	while (!q.empty()){
		pNode = q.front();
		q.pop_front();
		cout<<pNode->m_nData<<" ";
		if (pNode->m_pLeft){
			q.push_back(pNode->m_pLeft);
		}
		if (pNode->m_pRight){
			q.push_back(pNode->m_pRight);
		}
	}
}

int main()
{
	Node *node1 = new Node; node1->m_nData = 1;
	Node *node2 = new Node; node2->m_nData = 2;
	Node *node3 = new Node; node3->m_nData = 3;
	Node *node4 = new Node; node4->m_nData = 4;
	Node *node5 = new Node; node5->m_nData = 5;
	Node *node6 = new Node; node6->m_nData = 6;
	Node *node7 = new Node; node7->m_nData = 7;

	node1->m_pLeft = node2; node1->m_pRight = node3;
	node2->m_pLeft = node4; node2->m_pRight = node5;
	node3->m_pLeft = node6; node3->m_pRight = NULL;
	node4->m_pLeft = node7; node4->m_pRight = NULL;
	node5->m_pLeft = NULL; node5->m_pRight = NULL;
	node6->m_pLeft = NULL; node6->m_pRight = NULL;
	node7->m_pLeft = NULL; node7->m_pRight = NULL;

	/*          1
	           / \
		  2   3
		 / \ / 
		4  5 6
	       /
	      7
	*/

	traverseBinaryTreeByLevel(node1);
}