Clue Two fork Tree

When a binary tree is used as a storage structure, it takes a node to get the left child and the right child of the node, and can not directly get the precursor or successor of any of the nodes ' traversal sequences. But often we want to be more intuitive to know the predecessor of the node. The Clue two fork tree appears particularly important.

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The key to the clue two fork tree is to define a global variable to hold the last visited node.

node* prev;

(i) Pre-order clue two fork Tree

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void Prevordertag () {_prevordertag (_root);} void _prevordertag (node* root)//pre-order thread two fork tree {if (root = NULL) return;if (!root->_left) {Root->_lefttag = thread;root- >_left = prev;} if (prev &&!prev->_right) {Prev->_righttag = Thread;prev->_right = root;} Prev = root;if (Root->_lefttag = = link) _prevordertag (root->_left); if (Root->_righttag = = link) _prevordertag ( Root->_right);}

(ii) Middle sequence clue two fork tree

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void Midordertag () {_midordertag (_root);} void _midordertag (node* root)//middle order thread two fork tree {if (root = NULL) {return;} _midordertag (Root->_left); if (!root->_left) {Root->_lefttag = Thread;root->_left = prev;} if (prev&&!prev->_right) {Prev->_righttag = Thread;prev->_right = root;} Prev = Root;_midordertag (root->_right);}

(iii) Post-trail Clue two fork Tree

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void Rearordertag () {_rearordertag (_root);} void _rearordertag (node* root)//post-thread two fork tree {if (root = NULL) {return;} _rearordertag (Root->_left); _rearordertag (root->_right); if (!root->_left) {root->_lefttag = THREAD; Root->_left = prev;} if (prev&&!prev->_right) {Prev->_righttag = Thread;prev->_right = root;} prev = root;}

Clue Two fork Tree