Flatten Binary Tree to Linked List

Given a binary tree, flatten it to a linked list in-place.

For example,
Given

         1        /        2   5      /\        3   4   6

The flattened tree should look like:

   1         2             3                 4                     5                         6


Using the method of pre-order traversal to realize

voidFlatten (treenode*root) {    if(Root = =nullptr)return; Stack<TreeNode*>STA;    Sta.push (root); TreeNode* Lastroot =Root;  while(!Sta.empty ()) {Root=Sta.top (); if(Lastroot! = root->Right ) {            if(Lastroot! = root->Left ) {                if(Root->left! =nullptr) {Sta.push (Root-Left ); Continue; }            }            Else{TreeNode* Tempnode = root->Right ; Root->right =Lastroot; Root->left =nullptr; TreeNode* Endnode =Lastroot;  while(Endnode->right! =nullptr) Endnode= endnode->Right ; Endnode->right =Tempnode; }            if(Root->right! =nullptr) {Sta.push (Root-Right ); Continue; }} lastroot=Root;    Sta.pop (); }}

Methods that do not use traversal, that is, do not use a stack solution

voidFlatten (TreeNode *root) {TreeNode*now =Root;  while(now) {if(now->Left ) {            //Find Current node ' s prenode. Links to current node's right subtreetreenode* pre = now->Left ;  while(pre->Right ) {Pre= pre->Right ; } Pre->right = now->Right ; //Use the current node's left subtree to replace its right subtree (original right//subtree is already linked by current node ' s PrenodeNow->right = now->Left ; now->left =NULL; } Now= now->Right ; }}

Flatten Binary Tree to Linked List