All on the same line,

and am I being cited?

Weekly challenge 207 — 6 March 2023

Week 207 - 6 Mar 2023

Task 2

We are given a list of the number of citations a researcher has received for each of his published papers, ordered from most cited to least. We are asked to write a script to compute the researcher’s H-index, which is the maximum n where the n'th number in the list is at least n.

The logic behind this is not hard, but there are a few potential pitfalls. Firstly, the supplied array is zero-based, so we are looking for $array[$j + 1] being less than $j, and then the answer is $j - ie the preceding entry.

We need to allow for the case where the author has never been cited and the index is therefore zero - so he or she has an array of (0) or even () - and we need to remember the other edge case where all the papers have been cited enough - eg (4, 4, 4, 4);

I reckon the best solution is with a for loop with C-type parameters so that we preserve the loop variable $j on leaving the loop. I considered folding the 'if' condition into the second parameter of the 'for' and leaving the body of the 'for' loop empty:

for ($j = 0; $j < scalar @list and $list[$j] < $j + 1; $j ++) { }

but that relies on Perl evaluating the 'and' left to right which is perhaps unwise.

#!/usr/bin/perl # Peter Campbell Smith - 2023-02-20 use v5.28; use utf8; use warnings; # We are given a list of the number of citations a researcher has received # for each of his published papers, ordered from most cited to least. # We are asked to write a script to compute the researcher’s H-index, which is the maximum n # where the n'th number in the list is at least n. # Blog: http://ccgi.campbellsmiths.force9.co.uk/challenge/207/2 h_index(10, 8, 5, 4, 3); h_index(25, 8, 5, 3, 3); h_index(10, 9, 8, 7, 6, 5, 4, 3, 2, 1); h_index(0); h_index(); h_index(4, 4, 4, 4); sub h_index { my (@list, $j); # loop over list (0-based!) to find first where n'th number in list < $n @list = @_; for ($j = 0; $j < scalar @list; $j ++) { last unless $list[$j] >= $j + 1; } say qq[\nInput: \@citations = (] . join(', ', @list) . qq[)\nOutput: $j]; }

Input: @citations = (10, 8, 5, 4, 3) Output: 4 Input: @citations = (25, 8, 5, 3, 3) Output: 3 Input: @citations = (10, 9, 8, 7, 6, 5, 4, 3, 2, 1) Output: 5 Input: @citations = (0) Output: 0 Input: @citations = () Output: 0 Input: @citations = (4, 4, 4, 4) Output: 4

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Peter Campbell Smith is hereby placed in the public domain