Rank of the index

Question

Consider the following

What is the rank(index) of the node $50?$

Comments

In right skewed tree rank is $0?$

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According to the question, It could be zero-based or 1-based Indexing.

https://stackoverflow.com/questions/26080924/computing-rank-of-a-node-in-a-binary-search-tree

http://www.cs.princeton.edu/courses/archive/spr09/cos423/Lectures/rbtrees.pdf

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@lakshman

in right skewed tree rank of root is zero if u use 0 based rank