114. 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

Hints:

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

/**
* Definition for a binary tree node.
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
void flatten(TreeNode* root){
if(!root) return;
while(root){
if(root->left && root->right){
TreeNode* t = root->left;
while(t->right) t = t->right;
t->right = root->right;
root->right = NULL;
}
if(root->left){
root->right = root->left;
root->left = NULL;
}
root= root->right;
}
}
};