层次遍历二叉树

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《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

题目23: 层次遍历二叉树

题目: 从上到下打印二叉树的每个结点，同一层的结点按照从左到右的顺序打印。

#include <iostream>#include <exception>#include <queue>using namespace std;struct BinaryTreeNode{int                    m_nValue;BinaryTreeNode*        m_pLeft;BinaryTreeNode*        m_pRight;};BinaryTreeNode* ConstructCore(int* startPreorder, int* endPreorder, int* startInorder, int* endInorder);BinaryTreeNode* Construct(int* preorder, int* inorder, int length){if (preorder == NULL || inorder == NULL || length <= 0)return NULL;return ConstructCore(preorder, preorder + length - 1,inorder, inorder + length - 1);}BinaryTreeNode* ConstructCore(int* startPreorder, int* endPreorder,int* startInorder, int* endInorder){// 前序遍历序列的第一个数字是根结点的值int rootValue = startPreorder[0];BinaryTreeNode* root = new BinaryTreeNode();root->m_nValue = rootValue;root->m_pLeft = root->m_pRight = NULL;if (startPreorder == endPreorder){if (startInorder == endInorder && *startPreorder == *startInorder)return root;elsethrow std::exception("Invalid input.");}// 在中序遍历中找到根结点的值int* rootInorder = startInorder;while (rootInorder <= endInorder && *rootInorder != rootValue)++rootInorder;if (rootInorder == endInorder && *rootInorder != rootValue)throw std::exception("Invalid input.");int leftLength = rootInorder - startInorder;int* leftPreorderEnd = startPreorder + leftLength;if (leftLength > 0){// 构建左子树root->m_pLeft = ConstructCore(startPreorder + 1, leftPreorderEnd,startInorder, rootInorder - 1);}if (leftLength < endPreorder - startPreorder){// 构建右子树root->m_pRight = ConstructCore(leftPreorderEnd + 1, endPreorder,rootInorder + 1, endInorder);}return root;}void PrintFromTopToBottom(BinaryTreeNode* rRoot){if (rRoot == NULL)return;queue<BinaryTreeNode*> queueNode;queueNode.push(rRoot);while (!queueNode.empty()){BinaryTreeNode * pNode = queueNode.front();queueNode.pop();cout << pNode->m_nValue << " ";if (pNode->m_pLeft != nullptr)queueNode.push(pNode->m_pLeft);if (pNode->m_pRight != nullptr)queueNode.push(pNode->m_pRight);}}int main(){const int length = 8;int preorder[length] = { 1, 2, 4, 7, 3, 5, 6, 8 };int inorder[length] = { 4, 7, 2, 1, 5, 3, 8, 6 };BinaryTreeNode* root = nullptr;try{root = Construct(preorder, inorder, length);}catch (std::exception& exception){printf("Invalid Input.\n");}PrintFromTopToBottom(root);return 0;}

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