Created
March 15, 2020 19:59
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LCA algorithm with a parent pointer and a set to save time
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def find_lca(n1: BinaryTreeNode, n2: BinaryTreeNode) -> Optional[BinaryTreeNode]: | |
seen_on_path: Set[BinaryTreeNode] = set() | |
while n1 or n2: | |
# go up the tree at the same time | |
if n1: | |
# at every point check if we have already seen the node | |
if n1 in seen_on_path: | |
# first seen will be an ancestor | |
return n1 | |
seen_on_path.add(n1) | |
n1 = n1.parent | |
if n2: | |
if n2 in seen_on_path: | |
return n2 | |
seen_on_path.add(n2) | |
n2 = n2.parent | |
return None |
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