in reply to Better way of writing "find the missing number(s)"

Numbers 1..n, one missing. 

#! /usr/bin/perl -wl

use List::Util qw( sum );

my @arr = (1..3,5..7);

print +- sum -1-@arr .. -1,@arr;

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Re^2: Find the missing number
by pryrt (Abbot) on Apr 04, 2017 at 18:31 UTC

    inspired by your use of sum, the expected sum(1..n) = n*(n+1)/2, so take the found sum from the expected sum:

    use List::Util qw(sum);
my @arr=(1..3,5..7); 
print +(1+@arr)*(2+@arr)/2 - sum(@arr);

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    update: clarification = use 1+ and 2+ here because an element is missing from @arr

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Re^2: Find the missing number
by prysmatik (Sexton) on Apr 04, 2017 at 20:41 UTC

    That's a well oiled twist.

    Everyone looking at arrays and comparisons when there was a mathematical solution hiding in plain sight.

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      ... a mathematical solution hiding in plain sight.

      Perhaps better to say "hiding in obscurity." From the OP (emphasis added):

      ... find a missing number if in a list of numbers. ...

      ...
      my @arr = (19,17,22,23,24,15,16,25..35);
      ...

      But the list in the code example clearly has more than one missing number. See also the (current) thread title. I think the goose chase, although wild, was justified.

      Give a man a fish:  <%-{-{-{-<

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        Ahh, I stand corrected. It's funny how user requirements can hinge and swing wildly from a small misunderstanding.

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