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Lowest Common Ancestor in a Binary Search Tree.

Objec­tive: - Find the Low­est Com­mon Ances­tor of two given nodes in a Binary Search Tree

What is Low­est Com­mon Ancestor

In a given binary tree, The low­est com­mon ances­tor of two nodes n1 and n2 will be a node X such that node X will be the low­est node who has n1 and n2 as its descendants.

Sim­i­lar Prob­lem: Low­est Com­mon Ances­tor in a Binary Tree ( Not Binary Search Tree).




Input: A binary Search Tree and two nodes n1 and n2.


  1. Start will the root.
  2. If root>n1 and root>n2 then low­est com­mon ances­tor will be in left subtree.
  3. If root<n1 and root<n2 then low­est com­mon ances­tor will be in right subtree.
  4. If Step 2 and Step 3 is false then we are at the root which is low­est com­mon ances­tor, return it.


Com­plete Code:


Recursive-Lowest Common Ancestor of Nodes 5 and 14 is : 10
Iterative-Lowest Common Ancestor of Nodes 5 and 14 is : 10

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