this kata should be 6 kyu if the math at it was obvious.

Very nice kata! So many ways to solve it. I wanted to practice recursion so I did it using recursion.

Agree. Too easy for a 6 kyu

This kata looks straightforward initially but then you find out some clever constraints.

Agree

For an unordered linked list, one can simply add the seen elements in an array/list and skip the nodes where data is already in the seen list.

My rating: 'Very' satisfied.

Rated this 'Very' satisfied.

I rated it 'VERY' satisfied

This is a lot harder than 6 kyu, hence should be higher than 6 kyu. But that's just my opinion.

Use of map, filter, reduce etc.. should be made mandatory for learning purpose in my opinion.

One must not code while drunk.

Ah! coding while drunk. I like that.

Very clever kata

Very nice kata. Beginners will learn new concepts from this.