private int Depth(BinaryTreeNodeWithParent node)
{
int depth = 0;
while (node != null)
{
depth++;
node = node.Parent;
}
return(depth);
}
// Method2: Calculate depth
// Tx = O(h)
// Sx = O(1)
public BinaryTreeNodeWithParent LowestCommonAncestorUsingDepth(BinaryTreeNodeWithParent root,
BinaryTreeNodeWithParent p, BinaryTreeNodeWithParent q)
{
int p_depth = Depth(p);
int q_depth = Depth(q);
int diff_depth = p_depth - q_depth;
// q is located lower in the tree than p;
if (diff_depth < 0)
{
while (diff_depth < 0)
{
q = q.Parent;
diff_depth++;
}
}
else
{
while (diff_depth > 0)
{
p = p.Parent;
diff_depth--;
}
}
while (p != null && q != null)
{
if (p == q)
{
return(p);
}
p = p.Parent;
q = q.Parent;
}
return(null);
}
// Method1: Using hashset
public BinaryTreeNodeWithParent LowestCommonAncestor(BinaryTreeNodeWithParent root,
BinaryTreeNodeWithParent p, BinaryTreeNodeWithParent q)
{
HashSet <BinaryTreeNodeWithParent> visitedNodes = new HashSet <BinaryTreeNodeWithParent>();
while (p != null)
{
visitedNodes.Add(p);
p = p.Parent;
}
while (q != null)
{
if (visitedNodes.Contains(q))
{
return(q);
}
q = q.Parent;
}
return(null);
}