Flatten Binary Tree to Linked List

Flatten Binary Tree to Linked List  
Oct 14 '124412 / 13068

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

Hints:

If you notice carefully in the flattened tree, each node's right child points to the next node of a pre-order traversal.

 

其實就是前序走訪，在加上個隊尾指標。

/** * Definition for binary tree * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    TreeNode* Tail;    void preOrder(TreeNode* root)    {        if(root != NULL)        {            TreeNode* left = root->left;            TreeNode* right = root->right;            if(Tail == NULL){                Tail = root;            }            else{                if(Tail->right != root)                    Tail->right = root;                Tail->left = NULL;                Tail = root;            }            preOrder(left);            preOrder(right);        }    }    void flatten(TreeNode *root) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        Tail = NULL;        preOrder(root);    }};