二叉搜索树的非递归前中后序遍历 【微软面试100题 第四十三题】

题目要求：

　　实现二叉搜索树的前序、中序、后序非递归遍历。

题目分析：

　　非递归前序遍历：使用一个辅助栈，出栈一个结点并输出该结点，同时依次入栈该结点的右结点和左结点，再出栈，入栈...；

　　非递归中序遍历：使用一个辅助栈和一个临时结点，临时结点不断找树的左子树，知道为空，然后又跳到空结点父结点的右子树，又继续找右子树的左子树；

　　非递归后序遍历：使用两个辅助栈。

代码实现：

#include <iostream>#include <stack>using namespace std;typedef struct BinaryTree{    struct BinaryTree *left,*right;    int data;}BinaryTree;void initTree(BinaryTree **p);void PreOrderTree(BinaryTree *p);void InOrderTree(BinaryTree *p);void PostOrderTreeTraversal(BinaryTree *p);int main(void){    BinaryTree *root;    initTree(&root);    PreOrderTree(root);    InOrderTree(root);    PostOrderTreeTraversal(root);    return 0;}void PreOrderTree(BinaryTree *p){    stack<BinaryTree *> s;    s.push(p);    cout << "二叉搜索树的非递归前序遍历为：";    while(!s.empty())    {        BinaryTree *tmp = s.top();        cout << tmp->data << " ";        s.pop();        if(tmp->right)            s.push(tmp->right);        if(tmp->left)            s.push(tmp->left);    }    cout << endl;}void InOrderTree(BinaryTree *p){    stack<BinaryTree *> s;    BinaryTree *cur = p;    cout << "二叉搜索树的非递归中序遍历为：";    while(!s.empty() || cur!=NULL)    {        if(cur!=NULL)        {            s.push(cur);            cur = cur->left;        }        else        {            cur = s.top();            s.pop();            cout << cur->data << " ";            cur = cur->right;        }    }    cout << endl;}void PostOrderTreeTraversal(BinaryTree *p){    stack<BinaryTree *> sTraversal,sVisit;    sTraversal.push(p);    while(!sTraversal.empty())    {        BinaryTree *tmp = sTraversal.top();        sTraversal.pop();        sVisit.push(tmp);        if(tmp->left)            sTraversal.push(tmp->left);        if(tmp->right)            sTraversal.push(tmp->right);    }    cout << "二叉搜索树的非递归后序遍历:";    while(!sVisit.empty())    {        cout << sVisit.top()->data << " ";        sVisit.pop();    }    cout << endl;}//      10//     / \//    5   12//   / \//  4   7void initTree(BinaryTree **p){    *p = new BinaryTree;    (*p)->data = 10;     BinaryTree *tmpNode = new BinaryTree;    tmpNode->data = 5;    (*p)->left = tmpNode;     tmpNode = new BinaryTree;    tmpNode->data = 12;    (*p)->right = tmpNode;    tmpNode->left = NULL;    tmpNode->right = NULL;     BinaryTree *currentNode = (*p)->left;     tmpNode = new BinaryTree;    tmpNode->data = 4;    currentNode->left = tmpNode;    tmpNode->left = NULL;    tmpNode->right = NULL;     tmpNode = new BinaryTree;    tmpNode->data = 7;    currentNode->right = tmpNode;    tmpNode->left = NULL;    tmpNode->right = NULL;        cout << "二叉搜索树为：" <<endl;    cout << "     " << 10<<endl;    cout << "    " <<"/" << "  "<< "\\" <<endl;    cout << "   " << 5 << "    " << 12 << endl;    cout << " " <<"/" << "  "<< "\\" <<endl;    cout << 4 << "    " << 7 << endl;}