How to resolve the algorithm Successive prime differences step by step in the Prolog programming language

Published on 12 May 2024 09:40 PM
#Prolog

How to resolve the algorithm Successive prime differences step by step in the Prolog programming language

Table of Contents

Problem Statement

The series of increasing prime numbers begins: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, ... The task applies a filter to the series returning groups of successive primes, (s'primes), that differ from the next by a given value or values. Example 1: Specifying that the difference between s'primes be 2 leads to the groups: (Known as Twin primes or Prime pairs) Example 2: Specifying more than one difference between s'primes leads to groups of size one greater than the number of differences. Differences of 2, 4 leads to the groups: In the first group 7 is two more than 5 and 11 is four more than 7; as well as 5, 7, and 11 being successive primes. Differences are checked in the order of the values given, (differences of 4, 2 would give different groups entirely). Note: Generation of a list of primes is a secondary aspect of the task. Use of a built in function, well known library, or importing/use of prime generators from other Rosetta Code tasks is encouraged.

Let's start with the solution:

Step by Step solution about How to resolve the algorithm Successive prime differences step by step in the Prolog programming language

Source code in the prolog programming language

prime(2).     % use swi prolog
prime(N):-
	N /\ 1 > 0,              % odd
	M is floor(sqrt(N)) - 1, % reverse 2*I+1
	Max is M // 2,           % integer division
	forall(between(1, Max, I), N mod (2*I+1) > 0).

primesByDiffs([],_,[]).
primesByDiffs([Prime|Primes], Diff, [Slide|Slides]):-
	length(Diff, Len0),
	Len is Len0 + 1,
	length(Slide, Len),
	append(Slide, _, [Prime|Primes]),
	select(Diff, Slide),!,
	primesByDiffs(Primes, Diff, Slides).
primesByDiffs([_|Primes], Diff, Slides):-
	primesByDiffs(Primes, Diff, Slides).

select([],_).
select([Diff|Diffs],[S1, S2|Stail]):-
	S2 is S1 + Diff,
	select(Diffs, [S2|Stail]).

run([],_).
run([Diff|Dtail], PrimeList):-
	statistics(runtime,[Start|_]),
	primesByDiffs(PrimeList, Diff, SlideList),	
	length(SlideList, Num),
	statistics(runtime,[Stop|_]),
	Runtime is Stop - Start,
	SlideList = [First|SlideTail],
	format('~|~w~t~7+ number: ~|~t~d~4+ [time(ms) ~|~t~d~3+] first: ~|~w~t~22+',[Diff, Num, Runtime, First]),
	writeLast(SlideTail),!, nl,
	run(Dtail, PrimeList).

writeLast([]).
writeLast(SlideTail):-
	last(SlideTail, Last),
	format('last: ~w',[Last]).

do:-	Num is 1000000,
	statistics(runtime,[Start|_]),
	numlist(2, Num, List),
	include(prime, List, PrimeList),
	length(PrimeList, NumPrimes),
	statistics(runtime,[Stop|_]),
	RunTime is Stop - Start,
	format('there are ~w primes until ~w [time(ms) ~w]~n',[NumPrimes, Num, RunTime]),
	DiffList = [[1], [2], [2,2], [2,4], [4,2], [2,4,6],
		    [2,6,4], [4,2,6], [4,6,2], [6,2,4], [6,4,2]],
	run(DiffList, PrimeList).

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