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 isd
, the depth of each of its children isd + 1
. - The lowest common ancestor of a set
S
of nodes, is the nodeA
with the largest depth such that every node inS
is in the subtree with rootA
.
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.
Note: This question is the same as 865: https://leetcode.com/problems/smallest-subtree-with-all-the-deepest-nodes/
SOLUTION:
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, val=0, left=None, right=None):
# self.val = val
# self.left = left
# self.right = right
class Solution:
def maxDepth(self, root):
if root:
a = 1 + self.maxDepth(root.left)
b = 1 + self.maxDepth(root.right)
return max(a, b)
return -1
def lcaDeepestLeaves(self, root: Optional[TreeNode]) -> Optional[TreeNode]:
if root:
left = self.maxDepth(root.left)
right = self.maxDepth(root.right)
if left > right:
return self.lcaDeepestLeaves(root.left)
elif right > left:
return self.lcaDeepestLeaves(root.right)
else:
return root
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