https://github.com/jeff1evesque/interview-twitter

Least Common Ancestor
https://github.com/jeff1evesque/interview-twitter

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Least Common Ancestor

• Host: GitHub
• URL: https://github.com/jeff1evesque/interview-twitter
• Owner: jeff1evesque
• Created: 2014-05-08T00:21:01.000Z (over 10 years ago)
• Default Branch: master
• Last Pushed: 2014-05-12T02:18:04.000Z (over 10 years ago)
• Last Synced: 2024-10-30T03:54:52.237Z (2 months ago)
• Language: Python
• Homepage:
• Size: 617 KB
• Stars: 2
• Watchers: 2
• Forks: 0
• Open Issues: 10
• Metadata Files:
  • Readme: README.md

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README

        
Least Common Ancestor

=====================

I had an interactive interview with Twitter, and was given 15 minutes to write-up something that determined the least-common-ancestor for a binary search tree.  I am adjusting what I did for them -- but, feel free to use or improve what I have.

##Least Common Ancestor, written in Python

###Definition:

Suppose we let T be a rooted tree with n nodes. The lowest common ancestor between two nodes v and w is defined as the lowest node in T that has both v and w as descendants.

- http://en.wikipedia.org/wiki/Lowest_common_ancestor

###Overview:

This application will prompt users whether they want to input values interactively, or use a default file to import values.  The default import file is currently called `input.txt`.

##Input file

The values in the `input.txt` file must follow a special format:

```

root = [7]

tree = [23, 1, 14, 53, 22]

lca = [14, 53]

```

where `root` must be a list containing just one value (root of the binary search tree), `tree` an unordered list of values (remaining part of the binary search tree), and `lca` which must only contain two node values that is defined within the tree (either the root, or a tree node value).

##Interactive input:

Note: when users elect to interactively input values, the first value inputted will be considered the root.  Thus, if users input the following:

```

Enter tree value (q - to quit): 3

Enter tree value (q - to quit): 55

Enter tree value (q - to quit): 2

Enter tree value (q - to quit): 3

Enter tree value (q - to quit): 30

Enter tree value (q - to quit): 100

Enter tree value (q - to quit): 45

Enter tree value (q - to quit): 1

Enter tree value (q - to quit): 43

Enter tree value (q - to quit): 48

Enter tree value (q - to quit): 25

Enter tree value (q - to quit): 21

Enter tree value (q - to quit): q

```

then, the binary tree will have a representation as follows:

```

                 3

                / \

               /   \

              /     \

             2      55

            / \    /  \

           1   3  30   100

                 /  \

               25   45

               /   /  \

             21   43   48

```