Flatten Binary Tree to Linked List

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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

click to show hints.

Hints:

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


 The hints have stated clearly that each node's right child points to the next node of the pre-order traversal.


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


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