Medium
Quiz
#114 Flatten Binary Tree to Linked List
APPROACH
Rearrange the binary tree rooted at root into an in-place linked list:
- Reuse the same TreeNode class: the right pointer links to the next node and the left pointer must always be null.
- The resulting order must follow a pre-order traversal of the original 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]
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What is the optimal approach for this problem?