6.重建二叉树

#include <iostream>#include <exception>#include <queue>#include <stack>using namespace std;struct BinaryTreeNode{    int     m_nValue;    BinaryTreeNode* m_pLeft;    BinaryTreeNode* m_pRight;};BinaryTreeNode* ConstructCore(int* startPreorder, int* endPreorder, int* startInorder, int* endInorder){    //前序遍历的第一个数字是根节点的值    int rootValue = startPreorder[0];    BinaryTreeNode* root = new BinaryTreeNode();    root->m_nValue = rootValue;    root->m_pLeft = root->m_pRight = nullptr;    //这棵树仅有根节点一个节点    if(startPreorder == endPreorder)    {        if(startInorder == endInorder                && *startPreorder == *endInorder)        {            return root;        }        //else        //  throw std::exception("Invalid input.");    }    //在中序遍历中找到根节点的值    int* rootInorder = startInorder;    while(rootInorder <= endInorder && *rootInorder != rootValue)    {        ++ rootInorder;    }    //在中序遍历中没有找到根节点的值    if(rootInorder == endInorder && *rootInorder != rootValue)    {        //throw std::exception("invalid input.");    }    int leftLength = rootInorder - startInorder;    int* leftPreorderEnd = startPreorder + leftLength;    //构建左子树    if(leftLength >0)    {        root->m_pLeft = ConstructCore(startPreorder+1, leftPreorderEnd,                                      startInorder, rootInorder-1);    }    //构建右子树    if(leftLength < endPreorder-startPreorder)    {        root->m_pRight = ConstructCore(leftPreorderEnd+1, endPreorder,                                       rootInorder+1, endInorder);    }    return root;}BinaryTreeNode* Construct(int* preorder, int* inorder, int length){    return ConstructCore(preorder, preorder+length-1,                         inorder, inorder+length-1);};//先序遍历void Preorder(BinaryTreeNode* root){    if(root != nullptr)    {        cout<<root->m_nValue<<" ";        Preorder(root->m_pLeft);        Preorder(root->m_pRight);    }}//中序遍历void Inorder(BinaryTreeNode* root){    if(root != nullptr)    {        Inorder(root->m_pLeft);        cout<<root->m_nValue<<" ";        Inorder(root->m_pRight);    }}//后续void Postorder(BinaryTreeNode* root){    if(root != nullptr)    {        Postorder(root->m_pLeft);        Postorder(root->m_pRight);        cout<<root->m_nValue<<" ";    }}//层次遍历void Levelorder(BinaryTreeNode* root){    if(root == nullptr)        return;    queue<BinaryTreeNode*> nodes;    BinaryTreeNode* p = root;    nodes.push(p);    while(!nodes.empty())    {        p = nodes.front();        cout<<p->m_nValue<<" ";        nodes.pop();        if(p->m_pLeft != nullptr)            nodes.push(p->m_pLeft);        if(p->m_pRight != nullptr)            nodes.push(p->m_pRight);    }}//非递归先序遍历void NPreorder(BinaryTreeNode* root){    if(root == nullptr)        return ;    stack <BinaryTreeNode*> nodes;    nodes.push(root);    BinaryTreeNode* pNode = nullptr;    while(!nodes.empty())    {        pNode = nodes.top();        nodes.pop();        while(pNode)        {            cout<<pNode->m_nValue<<" "; //先访问左子树上的根            if(pNode->m_pRight) //右子树压栈                nodes.push(pNode->m_pRight);            pNode = pNode->m_pLeft; //左子树        }    }}//非递归中序遍历void NInorder(BinaryTreeNode* root){    if(root == nullptr)        return ;    stack<BinaryTreeNode*> nodes;    BinaryTreeNode* pNode = root;    while(!nodes.empty() || pNode != nullptr)    {        while(pNode)        {            nodes.push(pNode);            pNode = pNode->m_pLeft;        }        pNode = nodes.top();        nodes.pop();        cout<<pNode->m_nValue<<" ";        pNode = pNode->m_pRight;    }}int main(){    int preo[] = {1,2,4,7,3,5,6,8};    int ino[] =  {4,7,2,1,5,3,8,6};    BinaryTreeNode* root = Construct(preo, ino, sizeof(preo)/sizeof(preo[0]));    cout<<"先序遍历：";    Preorder(root);    cout<<endl<<"N先序遍历：";    Preorder(root);    cout<<endl<<"中序遍历：";    Inorder(root);    cout<<endl<<"N中序遍历：";    NInorder(root);    cout<<endl<<"后序遍历: ";    Inorder(root);    cout<<endl<<"层次遍历: ";    Levelorder(root);    return 0;}