一、题目
请实现一个函数按照之字形顺序打印二叉树,即第一行按照从左到右的顺序打印,第二层按照从右到左的顺序打印,第三行再按照从左到右的顺序打印,其他行以此类推。
二、关键
1.两个栈。
2.两个层的交替。
三、解释
1.解题思路:按之字形顺序打印二叉树需要两个栈。我们在打印某一层节点时,把下一层的子节点保存到相应的栈里。如果当前打印的是奇数层,则先保存左子节点再保存右子节点到第一个栈中。如果当前打印的是偶数层(第二层、第四层等),则先保存右子节点再保存左子节点到第二个栈中。
四、代码
#include <cstdio>
#include "..\Utilities\BinaryTree.h"
#include <stack>
void Print(BinaryTreeNode* pRoot)
{
if(pRoot == nullptr)
return;
std::stack<BinaryTreeNode*> levels[2]; //两个栈
int current = 0;
int next = 1;
levels[current].push(pRoot);
while(!levels[0].empty() || !levels[1].empty())
{
BinaryTreeNode* pNode = levels[current].top();
levels[current].pop();
printf("%d ", pNode->m_nValue);
if(current == 0)
{
if(pNode->m_pLeft != nullptr)
levels[next].push(pNode->m_pLeft);
if(pNode->m_pRight != nullptr)
levels[next].push(pNode->m_pRight);
}
else
{
if(pNode->m_pRight != nullptr)
levels[next].push(pNode->m_pRight);
if(pNode->m_pLeft != nullptr)
levels[next].push(pNode->m_pLeft);
}
//一层打印完毕
if(levels[current].empty())
{
printf("\n");
current = 1 - current; //**
next = 1 - next; //**
}
}
}
// ====================测试代码====================
// 8
// 6 10
// 5 7 9 11
void Test1()
{
BinaryTreeNode* pNode8 = CreateBinaryTreeNode(8);
BinaryTreeNode* pNode6 = CreateBinaryTreeNode(6);
BinaryTreeNode* pNode10 = CreateBinaryTreeNode(10);
BinaryTreeNode* pNode5 = CreateBinaryTreeNode(5);
BinaryTreeNode* pNode7 = CreateBinaryTreeNode(7);
BinaryTreeNode* pNode9 = CreateBinaryTreeNode(9);
BinaryTreeNode* pNode11 = CreateBinaryTreeNode(11);
ConnectTreeNodes(pNode8, pNode6, pNode10);
ConnectTreeNodes(pNode6, pNode5, pNode7);
ConnectTreeNodes(pNode10, pNode9, pNode11);
printf("====Test1 Begins: ====\n");
printf("Expected Result is:\n");
printf("8 \n");
printf("10 6 \n");
printf("5 7 9 11 \n\n");
printf("Actual Result is: \n");
Print(pNode8);
printf("\n");
DestroyTree(pNode8);
}
// 5
// 4
// 3
// 2
void Test2()
{
BinaryTreeNode* pNode5 = CreateBinaryTreeNode(5);
BinaryTreeNode* pNode4 = CreateBinaryTreeNode(4);
BinaryTreeNode* pNode3 = CreateBinaryTreeNode(3);
BinaryTreeNode* pNode2 = CreateBinaryTreeNode(2);
ConnectTreeNodes(pNode5, pNode4, nullptr);
ConnectTreeNodes(pNode4, pNode3, nullptr);
ConnectTreeNodes(pNode3, pNode2, nullptr);
printf("====Test2 Begins: ====\n");
printf("Expected Result is:\n");
printf("5 \n");
printf("4 \n");
printf("3 \n");
printf("2 \n\n");
printf("Actual Result is: \n");
Print(pNode5);
printf("\n");
DestroyTree(pNode5);
}
// 5
// 4
// 3
// 2
void Test3()
{
BinaryTreeNode* pNode5 = CreateBinaryTreeNode(5);
BinaryTreeNode* pNode4 = CreateBinaryTreeNode(4);
BinaryTreeNode* pNode3 = CreateBinaryTreeNode(3);
BinaryTreeNode* pNode2 = CreateBinaryTreeNode(2);
ConnectTreeNodes(pNode5, nullptr, pNode4);
ConnectTreeNodes(pNode4, nullptr, pNode3);
ConnectTreeNodes(pNode3, nullptr, pNode2);
printf("====Test3 Begins: ====\n");
printf("Expected Result is:\n");
printf("5 \n");
printf("4 \n");
printf("3 \n");
printf("2 \n\n");
printf("Actual Result is: \n");
Print(pNode5);
printf("\n");
DestroyTree(pNode5);
}
void Test4()
{
BinaryTreeNode* pNode5 = CreateBinaryTreeNode(5);
printf("====Test4 Begins: ====\n");
printf("Expected Result is:\n");
printf("5 \n\n");
printf("Actual Result is: \n");
Print(pNode5);
printf("\n");
DestroyTree(pNode5);
}
void Test5()
{
printf("====Test5 Begins: ====\n");
printf("Expected Result is:\n");
printf("Actual Result is: \n");
Print(nullptr);
printf("\n");
}
// 100
// /
// 50
// \
// 150
void Test6()
{
BinaryTreeNode* pNode100 = CreateBinaryTreeNode(100);
BinaryTreeNode* pNode50 = CreateBinaryTreeNode(50);
BinaryTreeNode* pNode150 = CreateBinaryTreeNode(150);
ConnectTreeNodes(pNode100, pNode50, nullptr);
ConnectTreeNodes(pNode50, nullptr, pNode150);
printf("====Test6 Begins: ====\n");
printf("Expected Result is:\n");
printf("100 \n");
printf("50 \n");
printf("150 \n\n");
printf("Actual Result is: \n");
Print(pNode100);
printf("\n");
}
// 8
// 4 12
// 2 6 10 14
// 1 3 5 7 9 11 13 15
void Test7()
{
BinaryTreeNode* pNode8 = CreateBinaryTreeNode(8);
BinaryTreeNode* pNode4 = CreateBinaryTreeNode(4);
BinaryTreeNode* pNode12 = CreateBinaryTreeNode(12);
BinaryTreeNode* pNode2 = CreateBinaryTreeNode(2);
BinaryTreeNode* pNode6 = CreateBinaryTreeNode(6);
BinaryTreeNode* pNode10 = CreateBinaryTreeNode(10);
BinaryTreeNode* pNode14 = CreateBinaryTreeNode(14);
BinaryTreeNode* pNode1 = CreateBinaryTreeNode(1);
BinaryTreeNode* pNode3 = CreateBinaryTreeNode(3);
BinaryTreeNode* pNode5 = CreateBinaryTreeNode(5);
BinaryTreeNode* pNode7 = CreateBinaryTreeNode(7);
BinaryTreeNode* pNode9 = CreateBinaryTreeNode(9);
BinaryTreeNode* pNode11 = CreateBinaryTreeNode(11);
BinaryTreeNode* pNode13 = CreateBinaryTreeNode(13);
BinaryTreeNode* pNode15 = CreateBinaryTreeNode(15);
ConnectTreeNodes(pNode8, pNode4, pNode12);
ConnectTreeNodes(pNode4, pNode2, pNode6);
ConnectTreeNodes(pNode12, pNode10, pNode14);
ConnectTreeNodes(pNode2, pNode1, pNode3);
ConnectTreeNodes(pNode6, pNode5, pNode7);
ConnectTreeNodes(pNode10, pNode9, pNode11);
ConnectTreeNodes(pNode14, pNode13, pNode15);
printf("====Test7 Begins: ====\n");
printf("Expected Result is:\n");
printf("8 \n");
printf("12 4 \n");
printf("2 6 10 14 \n");
printf("15 13 11 9 7 5 3 1 \n\n");
printf("Actual Result is: \n");
Print(pNode8);
printf("\n");
DestroyTree(pNode8);
}
int main(int argc, char* argv[])
{
Test1();
Test2();
Test3();
Test4();
Test5();
Test6();
Test7();
return 0;
}