ALGODAILY

January 23, 2021

“One of the laws of the professional jungle is that every dog has their day. Everyone gets a shot at the top and at some point someone else gets their turn.”

- Carla Harris

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Day 9: Lowest Common Ancestor

You're given a binary search tree and two of its child nodes as parameters. Can you write a method lowestCommonAncestor(root: Node, node1: Node, node2: Node) to identify the lowest common ancestor of the two nodes? The lowest common ancestor is the deepest node that has both of the two nodes as descendants.

In the below example, the lowest common ancestor of node 5 and 8 is 7.

/*
       7
      / \
     4   8
    / \
   1   5
*/

The method will called in the following manner: lowestCommonAncestor(root, node1, node2);.

You can assume our standard node definition for the tree vertices:

function Node(val) {
  this.val = val;
  this.left = this.right = null;
}

Constraints

• Number of nodes in the BST <= 1000
• The nodes will always contain integer values between -2147483648 and 2147483647
• Expected time complexity : O(n)
• Expected space complexity : O(1)

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