Flatten Binary Tree to Linked List

lc 114 Flatten Binary Tree to Linked List

iven 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

    public void flatten(TreeNode root) {
        if (root == null) return;

        TreeNode left = root.left;
        TreeNode right = root.right;

        root.left = null;

        flatten(left);
        flatten(right);

        root.right = left;
        TreeNode cur = root;
        while (cur.right != null) cur = cur.right;
        cur.right = right;        
    }