从上往下打印二叉树

题目：从上往下打印出二叉树的每个结点，同一层的结点按照从左到右的顺序打印。

struct BinaryTreeNode{
    int m_nValue;
    BinaryTreeNode* m_pLeft;
    BinaryTreeNode* m_pRight;
}

void PrintFromTopToBottom(BinaryTreeNode* pTreeRoot){
    if (!pTreeRoot){
        return;
    }

    std::deque<BinaryTreeNode *> dequeTreeNode;

    dequeTreeNode.push_back(pTreeRoot);

    while (dequeTreeNode.size()){
        BinaryTreeNode *pNode = dequeTreeNode.front();
        dequeTreeNode.pop_front();

        print("%d ", pNode->m_nValue);

        if (pNode->m_pLeft){
            dequeTreeNode.push_back(pNode->m_pLeft);
        }

        if (pNode->m_pRight){
        dequeTreeNode.push_back(pNode->m_pRight);
        }
    }
}

扩展：

• 广度优先遍历图