Leetcode 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

Difficulty: Medium

/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public void flatten(TreeNode root) {
if(root == null) return;
TreeNode curr = root;
while(curr != null){
if(curr.left != null){
TreeNode right = curr.right;
TreeNode tail = curr.left;
while(tail.right != null){
tail = tail.right;
}
curr.right = curr.left;
curr.left = null;
tail.right = right;
}
curr = curr.right;
}
return;
}
}