《剑指Offer》面试题23：从上往下打印二叉树

《剑指Offer》面试题23：从上往下打印二叉树

题目描述

    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。

解题思路

    按照层次遍历的方法，使用队列辅助。

    1.将根结点加入队列。

    2.循环出队，打印当前元素，若该结点有左子树，则将其加入队列，若有右子树，将其加入队列。

    3.直到队列为空，表明已经打印完所有结点。

测试用例

    功能测试（输入的二叉树既有左子树又有右子树，输入的二叉树仅有左子树或右子树，树中仅有一个结点）。

    特殊输入测试（输入NULL指针）。

代码

/*《剑指Offer——名企面试官精讲典型编程题》代码
著作权所有者：何海涛*/

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

struct BinaryTreeNode
{
	int m_nValue;
	BinaryTreeNode *m_pLeft;
	BinaryTreeNode *m_pRight;
};
BinaryTreeNode* CreateBinaryTreeNode(int value)
{
	BinaryTreeNode* pNode = new BinaryTreeNode();
	pNode->m_nValue = value;
	pNode->m_pLeft = NULL;
	pNode->m_pRight = NULL;

	return pNode;
}

void ConnectTreeNodes(BinaryTreeNode* pParent, BinaryTreeNode* pLeft, BinaryTreeNode* pRight)
{
	if (pParent != NULL)
	{
		pParent->m_pLeft = pLeft;
		pParent->m_pRight = pRight;
	}
}

void PrintTreeNode(BinaryTreeNode* pNode)
{
	if (pNode != NULL)
	{
		printf("value of this node is: %d\n", pNode->m_nValue);

		if (pNode->m_pLeft != NULL)
			printf("value of its left child is: %d.\n", pNode->m_pLeft->m_nValue);
		else
			printf("left child is null.\n");

		if (pNode->m_pRight != NULL)
			printf("value of its right child is: %d.\n", pNode->m_pRight->m_nValue);
		else
			printf("right child is null.\n");
	}
	else
	{
		printf("this node is null.\n");
	}

	printf("\n");
}

void PrintTree(BinaryTreeNode* pRoot)
{
	PrintTreeNode(pRoot);

	if (pRoot != NULL)
	{
		if (pRoot->m_pLeft != NULL)
			PrintTree(pRoot->m_pLeft);

		if (pRoot->m_pRight != NULL)
			PrintTree(pRoot->m_pRight);
	}
}

void DestroyTree(BinaryTreeNode* pRoot)
{
	if (pRoot != NULL)
	{
		BinaryTreeNode* pLeft = pRoot->m_pLeft;
		BinaryTreeNode* pRight = pRoot->m_pRight;

		delete pRoot;
		pRoot = NULL;

		DestroyTree(pLeft);
		DestroyTree(pRight);
	}
}


void PrintFromTopToBottom(BinaryTreeNode* pRoot)
{
	if (pRoot == NULL)
		return;

	deque<BinaryTreeNode *> dequeTreeNode;

	dequeTreeNode.push_back(pRoot);

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

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

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

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

// ====================测试代码====================
void Test(char* testName, BinaryTreeNode* pRoot)
{
	if (testName != NULL)
		printf("%s begins: \n", testName);

	PrintTree(pRoot);

	printf("The nodes from top to bottom, from left to right are: \n");
	PrintFromTopToBottom(pRoot);

	printf("\n\n");
}

//            10
//         /      \
//        6        14
//       /\        /\
//      4  8     12  16
void Test1()
{
	BinaryTreeNode* pNode10 = CreateBinaryTreeNode(10);
	BinaryTreeNode* pNode6 = CreateBinaryTreeNode(6);
	BinaryTreeNode* pNode14 = CreateBinaryTreeNode(14);
	BinaryTreeNode* pNode4 = CreateBinaryTreeNode(4);
	BinaryTreeNode* pNode8 = CreateBinaryTreeNode(8);
	BinaryTreeNode* pNode12 = CreateBinaryTreeNode(12);
	BinaryTreeNode* pNode16 = CreateBinaryTreeNode(16);

	ConnectTreeNodes(pNode10, pNode6, pNode14);
	ConnectTreeNodes(pNode6, pNode4, pNode8);
	ConnectTreeNodes(pNode14, pNode12, pNode16);

	Test("Test1", pNode10);

	DestroyTree(pNode10);
}

//               5
//              /
//             4
//            /
//           3
//          /
//         2
//        /
//       1
void Test2()
{
	BinaryTreeNode* pNode5 = CreateBinaryTreeNode(5);
	BinaryTreeNode* pNode4 = CreateBinaryTreeNode(4);
	BinaryTreeNode* pNode3 = CreateBinaryTreeNode(3);
	BinaryTreeNode* pNode2 = CreateBinaryTreeNode(2);
	BinaryTreeNode* pNode1 = CreateBinaryTreeNode(1);

	ConnectTreeNodes(pNode5, pNode4, NULL);
	ConnectTreeNodes(pNode4, pNode3, NULL);
	ConnectTreeNodes(pNode3, pNode2, NULL);
	ConnectTreeNodes(pNode2, pNode1, NULL);

	Test("Test2", pNode5);

	DestroyTree(pNode5);
}

// 1
//  \
//   2
//    \
//     3
//      \
//       4
//        \
//         5
void Test3()
{
	BinaryTreeNode* pNode1 = CreateBinaryTreeNode(1);
	BinaryTreeNode* pNode2 = CreateBinaryTreeNode(2);
	BinaryTreeNode* pNode3 = CreateBinaryTreeNode(3);
	BinaryTreeNode* pNode4 = CreateBinaryTreeNode(4);
	BinaryTreeNode* pNode5 = CreateBinaryTreeNode(5);

	ConnectTreeNodes(pNode1, NULL, pNode2);
	ConnectTreeNodes(pNode2, NULL, pNode3);
	ConnectTreeNodes(pNode3, NULL, pNode4);
	ConnectTreeNodes(pNode4, NULL, pNode5);

	Test("Test3", pNode1);

	DestroyTree(pNode1);
}

// 树中只有1个结点
void Test4()
{
	BinaryTreeNode* pNode1 = CreateBinaryTreeNode(1);
	Test("Test4", pNode1);

	DestroyTree(pNode1);
}

// 树中没有结点
void Test5()
{
	Test("Test5", NULL);
}

int main()
{
	Test1();
	Test2();
	Test3();
	Test4();
	Test5();
	system("pause");
	return 0;
}