编程练习-二叉树(父节点、非递归、O(0)空间)

1、一个有父节点的二叉树，不用递归和堆栈，遍历二叉树

思路是这样的，如果采用先序遍历的方法，首先遍历根节点，然后沿左子树下降，直到遍历到最左节点，此时返回最左节点的父节点，如果父节点的右子树非空，采用相同的方式遍历右子树，如果右子树已经比遍历完毕（通过parent->right == current来判断），那么向上回溯，如果当前节点一直来自于右子树，那么继续回溯，直到根节点或者节点不是右子树为止，如果当前节点不为空，那么继续回溯，在回溯的过程中判断回溯的节点的右子树是否为空，如果不为空，则遍历右子树，知道当前节点为空为止，也就是当前节点为根节点的父节点为止。

#include <stdio.h>template<typename T>class VisitFun { public:  virtual void operator()(const T& value) const = 0;  virtual void operator()(const T& value, const T& parent_value) const = 0;};class VisitFunInt : public VisitFun<int> { public:  virtual void operator()(const int& value) const {    printf("%d ", value);  }  virtual void operator()(const int& value, const int& parent_value) const {    printf("%d:%d ", value, parent_value);  }};template<typename T>class BinaryTree { private:  class TreeNode {   public:    TreeNode(const T& value, TreeNode* parent) : data_(value), left_(NULL), right_(NULL), parent_(parent) {}    T data_;    TreeNode* left_;    TreeNode* right_;    TreeNode* parent_;  }; public:  BinaryTree() : root_(NULL) {}  void Insert(const T& value) {    Insert(value, root_, NULL);  }  void InOrderVisit(const VisitFun<T>& visit_fun) {    TreeNode* current = VisitLeftMost(root_, visit_fun);    while (current) {      current = VisitBack(current, visit_fun);    }  }  void InOrderVisitRecursive(const VisitFun<T>& visit_fun) {    InOrderVisitRecursive(root_, visit_fun);  }   private:  void Insert(const T& value, TreeNode*& current, TreeNode* parent) {    if (current == NULL) {      current = new TreeNode(value, parent);    } else {      if (value >= current->data_) {        Insert(value, current->right_, current);      } else {        Insert(value, current->left_, current);      }    }  }  TreeNode* VisitLeftMost(TreeNode* current, const VisitFun<T>& visit_fun) {    TreeNode* parent = NULL;    while(current) {      visit_fun(current->data_);      parent = current;      current = current->left_;    }    return parent;  }  TreeNode* VisitBack(TreeNode* current, const VisitFun<T>& visit_fun) {    TreeNode* parent;    if (current->right_) {      return VisitLeftMost(current->right_, visit_fun);    }    parent = current->parent_;    while (parent && parent->right_ == current) {      current = parent;      parent = current->parent_;    }    return parent;  }  void InOrderVisitRecursive(TreeNode* current, const VisitFun<T>& visit_fun) {   if (current) {     if (current->parent_) {       visit_fun(current->data_, current->parent_->data_);     } else {       T tmp;       visit_fun(current->data_, tmp);     }        }   if (current->left_) {     InOrderVisitRecursive(current->left_, visit_fun);   }   if (current->right_) {     InOrderVisitRecursive(current->right_, visit_fun);   } }  TreeNode* root_;};int main(int argc, char** argv) {  int array[] = {3, 5, 2, 4, 7};  int array_size = sizeof(array) / sizeof(int);  VisitFunInt print_int;  BinaryTree<int> binary_tree;  for (int i = 0; i < array_size; ++i) {    binary_tree.Insert(array[i]);  }  //  binary_tree.InOrderVisitRecursive(print_int);  binary_tree.InOrderVisit(print_int);}

 参考：

http://www.winzp.org/blog/archives/406