114. Flatten Binary Tree to Linked List
Given the root of a binary tree, flatten the tree into a "linked list":
- The "linked list" should use the same TreeNode class where the right child pointer points to the next node in the list and the left child pointer is always null.
- The "linked list" should be in the same order as a pre-order traversal of the binary tree.
Example 1:
Input: root = [1,2,5,3,4,null,6]
Output: [1,null,2,null,3,null,4,null,5,null,6]
Example 2:
Input: root = []
Output: []
Example 3:
Input: root = [0]
Output: [0]
Constraints:
- The number of nodes in the tree is in the range [0, 2000].
- -100 <= Node.val <= 100
Follow up: Can you flatten the tree in-place (with O(1) extra space)?
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public void flatten(TreeNode root) {
while(root!=null){
if(root.left!=null){
TreeNode cur = root.left;
while(cur.right!=null){
cur = cur.right;
}
cur.right = root.right;
root.right = root.left;
root.left = null;
}
root = root.right;
}
}
}