ALGODAILY

July 30, 2021

“For all of the most important things, the timing always sucks. Waiting for a good time to quit your job? The stars will never align and the traffic lights of life will never all be green at the same time. The universe doesn't conspire against you, but it doesn't go out of its way to line up the pins either. Conditions are never perfect. "Someday" is a disease that will take your dreams to the grave with you. Pro and con lists are just as bad. If it's important to you and you want to do it "eventually," just do it and correct course along the way.”

- Tim Ferriss

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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 -1000000000 and 1000000000
• Expected time complexity : O(n)
• Expected space complexity : O(1)

Get the Solution →

Have you seen this question before? We are frequently adding problems and may have updated the order. You can change the day that you're on in the settings panel. As always, you can see the solution and a full step by step explanation at this link.

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Thanks,
Jake