Find lowest common ancestor in Binary Search Tree

Question

I\'ve got the following code to find the lowest common ancestor (the lowest node that has both a and b as descendants):

public static Node LCA(Node root, Node a,          


        

Answer 1

Just adding c# iterative version for finding common ancestor in Binary Search tree for reference:

public BinaryTreeNode BstLeastCommonAncestor(int e1, int e2)
    {
        //ensure both elements are there in the bst
        var n1 = this.BstFind(e1, throwIfNotFound: true);
        if(e1 == e2)
        {
            return n1;
        }
        this.BstFind(e2, throwIfNotFound: true);
        BinaryTreeNode leastCommonAcncestor = this._root;
        var iterativeNode = this._root;
        while(iterativeNode != null)
        {
            if((iterativeNode.Element > e1 ) && (iterativeNode.Element > e2))
            {
                iterativeNode = iterativeNode.Left;
            }
            else if((iterativeNode.Element < e1) && (iterativeNode.Element < e2))
            {
                iterativeNode = iterativeNode.Right;
            }
            else
            {
                //i.e; either iterative node is equal to e1 or e2 or in between e1 and e2
                return iterativeNode;
            }
        }

Where Find is defined as below

public BinaryTreeNode Find(int e, bool throwIfNotFound)
        {
            var iterativenode = this._root;
            while(iterativenode != null)
            {
                if(iterativenode.Element == e)
                {
                    return iterativenode;
                }
                if(e < iterativenode.Element)
                {
                    iterativenode = iterativenode.Left;
                }
                if(e > iterativenode.Element)
                {
                    iterativenode = iterativenode.Right;
                }
            }
            if(throwIfNotFound)
            {
                throw new Exception(string.Format("Given element {0} is not found", e);
            }
            return null;
        }

And BinaryTreeNode is defined as:

class BinaryTreeNode
    {
        public int Element;
        public BinaryTreeNode Left;
        public BinaryTreeNode Right;

    }

**tests**

[TestMethod]
        public void LeastCommonAncestorTests()
        {
            int[] a = { 13, 2, 18, 1, 5, 17, 20, 3, 6, 16, 21, 4, 14, 15, 25, 22, 24 };
            int[] b = { 13, 13, 13, 2, 13, 18, 13, 5, 13, 18, 13, 13, 14, 18, 25, 22};
            BinarySearchTree bst = new BinarySearchTree();
            foreach (int e in a)
            {
                bst.Add(e);
                bst.Delete(e);
                bst.Add(e);
            }
            for(int i = 0; i < b.Length; i++)
            {
                var n = bst.BstLeastCommonAncestor(a[i], a[i + 1]);
                Assert.IsTrue(n.Element == b[i]);
            }
        }