User
freespace tweets, referring to formulation of our
free demo task:
@Codility your equivalent point definition is broken. The left hand sum is from i=0 to k-1, and you have k=0 is a valid solution... [link]
... therefore, the left hand sum is from 0 to -1, and is invalid. You guys can learn a thing or two from reading ACM problems [link]
Having worked a lot on ACM problems, we would have not written this blog post, if not the last sentence, thanks for getting us going! :-) The author of the tweet refers to this expression:
which is another way of writing this summation:
He/she claims that the above expression is ill-defined for
k=0. Let's look into
The Holy Scripture, chapter 1.2.3
Sums and Products, verse 1:
Clearly, when no integer
i satisfies the condition
0<=i<=k-1 (which is written here in an alternate form mentioned by The Scripture, namely
i=0 in subscript and
k-1 in superscript), we end up with a sum of an empty sequence, which Master
Donald Knuth assumes to be equal zero (and we additionally restate the latter assumption in the problem description). So for k=0 the (empty) sum is well-defined and equals 0.
which is another way of writing this summation:
He/she claims that the above expression is ill-defined for k=0. Let's look into The Holy Scripture, chapter 1.2.3 Sums and Products, verse 1:
Clearly, when no integer i satisfies the condition 0<=i<=k-1
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