- Difficulty: Medium
- Tags: LeetCode, Medium, Tree, Depth-First Search, Binary Tree, leetcode-1666, O(h), O(1), 🔒
Problem
Given the root of a binary tree and a leaf node, reroot the tree so that the leaf is the new root.
You can reroot the tree with the following steps for each node cur on the path starting from the leaf up to the root​​​ excluding the root:
- If
curhas a left child, then that child becomescur's right child. cur's original parent becomescur's left child. Note that in this process the original parent's pointer tocurbecomesnull, making it have at most one child.
Return the new root of the rerooted tree.
Note: Ensure that your solution sets the Node.parent pointers correctly after rerooting or you will receive "Wrong Answer".
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Example 1:
Input: root = [3,5,1,6,2,0,8,null,null,7,4], leaf = 7 Output: [7,2,null,5,4,3,6,null,null,null,1,null,null,0,8]
Example 2:
Input: root = [3,5,1,6,2,0,8,null,null,7,4], leaf = 0 Output: [0,1,null,3,8,5,null,null,null,6,2,null,null,7,4]
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Constraints:
- The number of nodes in the tree is in the range
[2, 100]. -109 <= Node.val <= 109- All
Node.valare unique. leafexist in the tree.