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Given the root
of a binary tree, return the lowest common ancestor of its deepest leaves.
Recall that:
- The node of a binary tree is a leaf if and only if it has no children
- The depth of the root of the tree is
0
. if the depth of a node is d
, the depth of each of its children is d + 1
.
- The lowest common ancestor of a set
S
of nodes, is the node A
with the largest depth such that every node in S
is in the subtree with root A
.
Note: This question is the same as 865: https://leetcode.com/problems/smallest-subtree-with-all-the-deepest-nodes/
Example 1:
Input: root = [3,5,1,6,2,0,8,null,null,7,4]
Output: [2,7,4]
Explanation: We return the node with value 2, colored in yellow in the diagram.
The nodes coloured in blue are the deepest leaf-nodes of the tree.
Note that nodes 6, 0, and 8 are also leaf nodes, but the depth of them is 2, but the depth of nodes 7 and 4 is 3.
Example 2:
Input: root = [1]
Output: [1]
Explanation: The root is the deepest node in the tree, and it's the lca of itself.
Example 3:
Input: root = [0,1,3,null,2]
Output: [2]
Explanation: The deepest leaf node in the tree is 2, the lca of one node is itself.
Constraints:
- The number of nodes in the tree will be in the range
[1, 1000]
.
0 <= Node.val <= 1000
- The values of the nodes in the tree are unique.
[Tree]
[Depth-first Search]
Hints
Hint 1
Do a postorder traversal.
Hint 2
Then, if both subtrees contain a deepest leaf, you can mark this node as the answer (so far).
Hint 3
The final node marked will be the correct answer.