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1218. Lowest Common Ancestor of Deepest Leaves

My accepted Python solution to LeetCode problem 1218, Lowest Common Ancestor of Deepest Leaves, running in 1ms.

  • Difficulty: Medium
  • Python
  • Runtime 1ms
  • Memory 17.6MB

Read the problem on LeetCode View on GitHub

The problem statement is LeetCode’s and stays on their site. What follows is my accepted solution.

Python

Accepted on LeetCode — runtime 1ms, memory 17.6MB, accepted 2026-01-02.

python
# 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 lcaDeepestLeaves(self, root: Optional[TreeNode]) -> Optional[TreeNode]:
        def dfs(node):
            # Returns (depth, lca_node)
            if not node:
                return (0, None)
            
            left_depth, left_lca = dfs(node.left)
            right_depth, right_lca = dfs(node.right)
            
            if left_depth > right_depth:
                return (left_depth + 1, left_lca)
            elif right_depth > left_depth:
                return (right_depth + 1, right_lca)
            else:
                # Equal depths - current node is the LCA
                return (left_depth + 1, node)
        
        return dfs(root)[1]

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