Amicable pairs: Difference between revisions
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(→{{header|ALGOL 68}}: Better search algorithm, as in e.g., the PLI-80 sample (but still using a table of divisor sums)) |
(→{{header|PL/I-80}}: Added alternative version using a table of proper divisor sums) |
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==={{header|PL/I-80}}===
====Computing the divisor sum on the fly====
Rather than populating an array with the sum of the proper divisors and then searching, the approach here calculates them on the fly as needed, saving memory, and avoiding a noticeable lag on program startup on the ancient systems that hosted PL/I-80.
<syntaxhighlight lang="pl/i">
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8 pairs were found
</pre>
====Without using division/modulo====
<syntaxhighlight lang="pl/i">
amicable: procedure options (main);
%replace
search_limit by 20000;
dcl sumf( 1 : search_limit ) fixed bin;
dcl (a, b, found) fixed bin;
put skip list ('Searching for amicable pairs up to ');
put edit (search_limit) (f(5));
do a = 1 to search_limit; sumf( a ) = 1; end;
do a = 2 to search_limit;
do b = a + a to search_limit by a;
sumf( b ) = sumf( b ) + a;
end;
end;
found = 0;
do a = 2 to search_limit;
b = sumf(a);
if (b > a) then
do;
if (sumf(b) = a) then
do;
found = found + 1;
put skip edit (a,b) (f(7));
end;
end;
end;
put skip list (found, ' pairs were found');
stop;
end amicable;
</syntaxhighlight>
{{out}}
Same as the other PLI-80 sample.
=={{header|PL/M}}==
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