diff options
43 files changed, 2846 insertions, 1848 deletions
diff --git a/challenge-147/alexander-karelas/perl/ch-2.pl b/challenge-147/alexander-karelas/perl/ch-2.pl new file mode 100755 index 0000000000..b6548da74a --- /dev/null +++ b/challenge-147/alexander-karelas/perl/ch-2.pl @@ -0,0 +1,30 @@ +#!/usr/bin/env perl + +use v5.32; +use warnings; + +use experimental 'signatures'; + +my @cache; +my %cache; +sub get_nth_pentagon_number ($n) { + my $pentagon = $cache[$n]; + $pentagon //= do { + $cache[$n] = $n * (3 * $n - 1) / 2; + $cache{ $cache[$n] } = $n; + } +} + +for (my $i = 1; ; $i++) { + my $ith = get_nth_pentagon_number($i); + get_nth_pentagon_number(2 * $i - 1); + get_nth_pentagon_number(2 * $i); + for (my $j = 1; $j < $i; $j++) { + my $jth = get_nth_pentagon_number($j); + if (exists $cache{$ith + $jth} and exists $cache{$ith - $jth}) { + say "P($i) + P($j) = $ith + $jth = @{[ $ith + $jth ]} = P(", $cache{$ith + $jth}, ")"; + say "P($i) - P($j) = $ith - $jth = @{[ $ith - $jth ]} = P(", $cache{$ith - $jth}, ")"; + exit; + } + } +} diff --git a/challenge-147/dave-jacoby/blog.txt b/challenge-147/dave-jacoby/blog.txt new file mode 100644 index 0000000000..e386698c3c --- /dev/null +++ b/challenge-147/dave-jacoby/blog.txt @@ -0,0 +1 @@ +https://jacoby.github.io/2022/01/11/truncations-and-pentagons-the-weekly-challenge-147.html
\ No newline at end of file diff --git a/challenge-147/dave-jacoby/perl/ch-1.pl b/challenge-147/dave-jacoby/perl/ch-1.pl new file mode 100644 index 0000000000..197c72f5b7 --- /dev/null +++ b/challenge-147/dave-jacoby/perl/ch-1.pl @@ -0,0 +1,35 @@ +#!/usr/bin/env perl + +use strict; +use warnings; +use feature qw{ say postderef signatures state }; +no warnings qw{ experimental }; + +my %primes; +my %trunc; +my $c = 1; +my $n = 2; + +while (1) { + if ( $n !~ /0/mx && is_prime($n) ) { + $primes{$n}++; + my $copy = $n; + while ( length $copy > 0 ) { + last unless $primes{$copy}; + substr( $copy, 0, 1 ) = ''; + if ( $copy eq '' ) { + $trunc{$n}++ if $copy eq ''; + last; + } + } + last if scalar keys %trunc > 30; + } + $n++; +} + +say join ', ', sort { $a <=> $b } keys %trunc; + +sub is_prime ($n) { + for ( 2 .. sqrt $n ) { return unless $n % $_ } + return 1; +} diff --git a/challenge-147/dave-jacoby/perl/ch-2.pl b/challenge-147/dave-jacoby/perl/ch-2.pl new file mode 100644 index 0000000000..61f3b1b1d6 --- /dev/null +++ b/challenge-147/dave-jacoby/perl/ch-2.pl @@ -0,0 +1,35 @@ +#!/usr/bin/env perl + +use strict; +use warnings; +use feature qw{ say postderef signatures state }; +no warnings qw{ experimental }; + +my $top = 10_000; +my @pentagon = map { pentagon($_) } 0 .. $top; +my %pentagon = map { $_ => 1 } @pentagon; +delete $pentagon{0}; + +for my $i ( 1 .. $top ) { + for my $j ( 1 .. $i ) { + my $pi = $pentagon[$i]; + my $pj = $pentagon[$j]; + my $sum = $pi + $pj; + if ( $pentagon{$sum} ) { + my $product = abs( $pi - $pj ); + if ( $pentagon{$product} ) { + say <<"END"; + P($i) = $pi + P($j) = $pj + $pi + $pj = $sum + abs( $pi - $pj ) = $product +END + exit; + } + } + } +} + +sub pentagon ( $n ) { + return $n * ( ( $n * 3 ) - 1 ) / 2; +} diff --git a/challenge-147/eric-cheung/excel-vba/Challenge_147.xlsm b/challenge-147/eric-cheung/excel-vba/Challenge_147.xlsm Binary files differnew file mode 100755 index 0000000000..6f7427aff8 --- /dev/null +++ b/challenge-147/eric-cheung/excel-vba/Challenge_147.xlsm diff --git a/challenge-147/eric-cheung/excel-vba/ch-1.bas b/challenge-147/eric-cheung/excel-vba/ch-1.bas new file mode 100755 index 0000000000..558dd6656c --- /dev/null +++ b/challenge-147/eric-cheung/excel-vba/ch-1.bas @@ -0,0 +1,86 @@ +Attribute VB_Name = "ModTask_01"
+Option Explicit
+
+Public Const strMyTitle As String = "Eric Cheung"
+
+Option Base 1
+Public nPrimeArr() As Long
+Public nPrimeCnt As Integer
+
+Function IsPrime(nInput As Integer) As Boolean
+
+ Dim nNumLoop As Integer
+
+ If nInput = 1 Then
+ IsPrime = False
+ Exit Function
+ End If
+
+ For nNumLoop = LBound(nPrimeArr) To UBound(nPrimeArr)
+ If nInput = nPrimeArr(nNumLoop) Then
+ IsPrime = True
+ Exit Function
+ ElseIf nInput Mod nPrimeArr(nNumLoop) = 0 Then
+ IsPrime = False
+ Exit Function
+ End If
+ Next nNumLoop
+
+ IsPrime = True
+
+End Function
+
+Function IsTruncatablePrime(nInput As Integer) As Boolean
+
+ If nInput = 0 Then
+ IsTruncatablePrime = False
+ Exit Function
+ ElseIf Not IsPrime(nInput) Then
+ IsTruncatablePrime = False
+ Exit Function
+ End If
+
+ nPrimeCnt = nPrimeCnt + 1
+ ReDim Preserve nPrimeArr(1 To nPrimeCnt)
+ nPrimeArr(nPrimeCnt) = nInput
+
+ If nInput < 10 Then
+ IsTruncatablePrime = True
+ Else
+ If Val(Mid(CStr(nInput), 2, 1)) = 0 Then
+ IsTruncatablePrime = False
+ Exit Function
+ End If
+ IsTruncatablePrime = IsTruncatablePrime(Val(Right(CStr(nInput), Len(CStr(nInput)) - 1)))
+ End If
+
+End Function
+
+Sub Task_01()
+
+ Const nTruncatablePrimeCntMax As Integer = 20
+
+ Dim nLoop As Integer, nTruncatablePrimeCnt As Integer
+ Dim strMsg As String
+
+ ReDim nPrimeArr(1 To 1)
+
+ nPrimeCnt = 1
+ nPrimeArr(1) = 2
+ nLoop = 3
+
+ nTruncatablePrimeCnt = 1
+
+ strMsg = "First " & nTruncatablePrimeCntMax & " left-truncatable prime numbers in base 10 are: " & 2
+
+ Do While (nTruncatablePrimeCnt < nTruncatablePrimeCntMax)
+ If IsTruncatablePrime(nLoop) Then
+ strMsg = strMsg & ", " & nLoop
+ nTruncatablePrimeCnt = nTruncatablePrimeCnt + 1
+ End If
+ nLoop = nLoop + 1
+ Loop
+
+ MsgBox strMsg, vbOKOnly, strMyTitle
+
+End Sub
diff --git a/challenge-147/eric-cheung/python/ch-2.py b/challenge-147/eric-cheung/python/ch-2.py new file mode 100755 index 0000000000..6a716b2ddd --- /dev/null +++ b/challenge-147/eric-cheung/python/ch-2.py @@ -0,0 +1,45 @@ +## Remarks
+## https://www.mathblog.dk/project-euler-44-smallest-pair-pentagonal-numbers/
+## https://radiusofcircle.blogspot.com/2016/06/problem-44-project-euler-solution-with-python.html
+## http://radiusofcircle.blogspot.com
+
+## Time Module for Calculating Execution Time
+import time
+
+## Time At The Start of Program Execution
+dStartTime = time.time()
+
+def is_pentagonal(nInput):
+ ## Function To Check If The Number is Pentagonal Number or Not
+ if (1 + (24 * nInput + 1) ** 0.5) % 6 == 0:
+ return True
+ return False
+
+## Flag To Check If The Number Is Found Or Not
+bFlag = True
+
+# While Loop Iterator
+nLoop = 1
+
+# While Loop
+while bFlag:
+ nNum_01 = nLoop * (3 * nLoop - 1) / 2
+ for nSubLoop in range(1, nLoop):
+ nNum_02 = nSubLoop * (3 * nSubLoop - 1) / 2
+ if is_pentagonal(nNum_01 + nNum_02) and is_pentagonal(nNum_01 - nNum_02):
+ print ("nLoop = " + str(nLoop) + ", nSubLoop = " + str(nSubLoop))
+ bFlag = False
+ break
+ nLoop = nLoop + 1
+
+# Time At The End of Program Execution
+dEndTime = time.time()
+
+# Printing The Total Time For Execution
+print ("Time Needed: " + str(dEndTime - dStartTime))
+
+
+## Result
+## nLoop = 2167, nSubLoop = 1020
+## Time Needed: 1.1174473762512207
+
diff --git a/challenge-147/luca-ferrari/blog-1.txt b/challenge-147/luca-ferrari/blog-1.txt index af17183edb..f5a4859575 100644 --- a/challenge-147/luca-ferrari/blog-1.txt +++ b/challenge-147/luca-ferrari/blog-1.txt @@ -1 +1 @@ -https://fluca1978.github.io/2022/01/04/PerlWeeklyChallenge146.html#task1 +https://fluca1978.github.io/2022/01/10/PerlWeeklyChallenge147.html#task1 diff --git a/challenge-147/luca-ferrari/blog-2.txt b/challenge-147/luca-ferrari/blog-2.txt index 5e5d379514..c3a26988bb 100644 --- a/challenge-147/luca-ferrari/blog-2.txt +++ b/challenge-147/luca-ferrari/blog-2.txt @@ -1 +1 @@ -https://fluca1978.github.io/2022/01/04/PerlWeeklyChallenge146.html#task2 +https://fluca1978.github.io/2022/01/10/PerlWeeklyChallenge147.html#task2 diff --git a/challenge-147/luca-ferrari/blog-3.txt b/challenge-147/luca-ferrari/blog-3.txt index aa716b41b9..1854457738 100644 --- a/challenge-147/luca-ferrari/blog-3.txt +++ b/challenge-147/luca-ferrari/blog-3.txt @@ -1 +1 @@ -https://fluca1978.github.io/2022/01/04/PerlWeeklyChallenge146.html#task1pg +https://fluca1978.github.io/2022/01/10/PerlWeeklyChallenge146.html#task1pg diff --git a/challenge-147/luca-ferrari/blog-4.txt b/challenge-147/luca-ferrari/blog-4.txt index 520b859582..63d8983e4e 100644 --- a/challenge-147/luca-ferrari/blog-4.txt +++ b/challenge-147/luca-ferrari/blog-4.txt @@ -1 +1 @@ -https://fluca1978.github.io/2022/01/04/PerlWeeklyChallenge146.html#task2pg +https://fluca1978.github.io/2022/01/10/PerlWeeklyChallenge147.html#task2pg diff --git a/challenge-147/luca-ferrari/blog-5.txt b/challenge-147/luca-ferrari/blog-5.txt new file mode 100644 index 0000000000..b872164f21 --- /dev/null +++ b/challenge-147/luca-ferrari/blog-5.txt @@ -0,0 +1 @@ +https://fluca1978.github.io/2022/01/10/PerlWeeklyChallenge147.html#task2pgb diff --git a/challenge-147/luca-ferrari/postgresql/ch-2.sql b/challenge-147/luca-ferrari/postgresql/ch-2.sql index 61465a21c6..67ed7cdeb3 100644 --- a/challenge-147/luca-ferrari/postgresql/ch-2.sql +++ b/challenge-147/luca-ferrari/postgresql/ch-2.sql @@ -66,8 +66,6 @@ BEGIN IF FOUND THEN SELECT current_tuple.n , other_tuple.n - , current_tuple.p - , other_tuple.p , current_tuple.p + other_tuple.p , abs( current_tuple.p - other_tuple.p ) , p1.n diff --git a/challenge-147/luca-ferrari/postgresql/ch-2b.sql b/challenge-147/luca-ferrari/postgresql/ch-2b.sql new file mode 100644 index 0000000000..427419b900 --- /dev/null +++ b/challenge-147/luca-ferrari/postgresql/ch-2b.sql @@ -0,0 +1,46 @@ +CREATE OR REPLACE FUNCTION +f_pentagon( n bigint ) +RETURNS bigint +AS +$CODE$ + SELECT ( n * ( 3 * n - 1 ) / 2 ); +$CODE$ +LANGUAGE sql +IMMUTABLE; + +/* +pentagon_pairs +---------------- +1020, 2167 +2167, 1020 +(2 rows) + +Time: 5820,066 ms (00:05,820) + +*/ +WITH RECURSIVE pentagons( n, p ) +AS +( + SELECT 1 AS n + , f_pentagon( 1 ) AS p + +UNION + SELECT p.n + 1 + , f_pentagon( p.n + 1 ) + FROM pentagons p + WHERE p.n < 5000 +) + +SELECT format( '%s, %s', l.n, r.n ) AS pentagon_pairs +FROM pentagons l, pentagons r +WHERE EXISTS( + SELECT * + FROM pentagons ps + WHERE ps.p = l.p + r.p + ) +AND EXISTS ( + SELECT * + FROM pentagons ps + WHERE ps.p = abs( l.p - r.p ) + ) +; diff --git a/challenge-147/perlboy1967/perl/ch-1.pl b/challenge-147/perlboy1967/perl/ch-1.pl new file mode 100755 index 0000000000..2fbd74581f --- /dev/null +++ b/challenge-147/perlboy1967/perl/ch-1.pl @@ -0,0 +1,40 @@ +#!/bin/perl + +=pod + +The Weekly Challenge - 147 + - https://perlweeklychallenge.org/blog/perl-weekly-challenge-147/#TASK1 + +Author: Niels 'PerlBoy' van Dijke + +TASK #1 › Truncatable Prime +Submitted by: Mohammad S Anwar + +Write a script to generate first 20 left-truncatable prime numbers in base 10. + + || In number theory, a left-truncatable prime is a prime number which, in a + || given base, contains no 0, and if the leading left digit is successively + || removed, then all resulting numbers are primes. + +=cut + +use v5.16; + +use Math::Primality qw(next_prime); + +my @tPrimes; +my %primes; + +my $n = 1; +do { + $n = next_prime($n); + $primes{$n}++; + + if (index($n,0)<0) { + my $p = $n; + 1 while ($p =~ s#^.## && exists $primes{$p}); + push(@tPrimes,$n) if ($p eq ''); + } +} while (scalar @tPrimes < 20); + +printf "%s\n", join(',',@tPrimes); diff --git a/challenge-147/perlboy1967/perl/ch-2.pl b/challenge-147/perlboy1967/perl/ch-2.pl new file mode 100755 index 0000000000..9a96d111c4 --- /dev/null +++ b/challenge-147/perlboy1967/perl/ch-2.pl @@ -0,0 +1,56 @@ +#!/bin/perl + +=pod + +The Weekly Challenge - 147 + - https://perlweeklychallenge.org/blog/perl-weekly-challenge-147/#TASK2 + +Author: Niels 'PerlBoy' van Dijke + +TASK #2 › Pentagon Numbers +Submitted by: Mohammad S Anwar + +Write a sript to find the first pair of Pentagon Numbers whose sum and difference +are also a Pentagon Number. + + || Pentagon numbers can be defined as P(n) = n(3n - 1)/2. + + +=cut + +use v5.16; + +sub pentagonNumber($) { + $_[0]*(3*$_[0]-1) >> 1; +} + +my @p = (undef); +my %pIdx; + +my $i = 1; + +while (1) { + push(@p,pentagonNumber scalar @p); + $pIdx{$p[-1]} = scalar @p - 1; + + foreach my $j (1 .. $i-1) { + my $dif = $p[$i] - $p[$j]; + next if !exists $pIdx{$dif}; + + my $sum = $p[$i] + $p[$j]; + + while ($p[-1] <= $sum) { + push(@p,pentagonNumber scalar @p); + $pIdx{$p[-1]} = scalar @p - 1; + } + + if (exists $pIdx{$sum}) { + printf "P(%d) + P(%d) = %d + %d = %d = P(%d)\n", + $i, $j, $p[$i], $p[$j], $sum, $pIdx{$sum}; + printf "P(%d) - P(%d) = %d - %d = %d = P(%d)\n", + $i, $j, $p[$i], $p[$j], $dif, $pIdx{$dif}; + exit; + } + } + $i++; +} diff --git a/challenge-147/peter-campbell-smith/blog.txt b/challenge-147/peter-campbell-smith/blog.txt new file mode 100644 index 0000000000..78e76441f9 --- /dev/null +++ b/challenge-147/peter-campbell-smith/blog.txt @@ -0,0 +1 @@ +https://pjcs-pwc.blogspot.com/2022/01/chop-off-their-heads-and-conquer.html diff --git a/challenge-147/peter-campbell-smith/perl/ch-1.pl b/challenge-147/peter-campbell-smith/perl/ch-1.pl new file mode 100755 index 0000000000..0a3901fe78 --- /dev/null +++ b/challenge-147/peter-campbell-smith/perl/ch-1.pl @@ -0,0 +1,70 @@ +#!/usr/bin/perl + +# Peter Campbell Smith - 2022-01-10 +# PWC 147 task 1 + +use v5.28; +use warnings; +use strict; + +# Write a script to generate first 20 left-truncatable prime numbers in base 10. +# In number theory, a left-truncatable prime is a prime number which, in a given base, +# contains no 0, and if the leading left digit is successively removed, then all +# resulting numbers are primes. + +# Note that the last digit cannot be 2, 4, 5, 6, 8, 0 as no primes end with those +# and cannot be 9 as when all the preceding digits are removed, 9 is not prime, +# so the last digit can only be 1, 3 or 7. + +# The definition above speaks of 'all resulting numbers' so I am ruling out +# single-digit prime numbers as they have no 'resulting numbers' when the +# leftmost digit is removed. + +my ($seeking, $prime_index, $from, $to, $test, $this, @not_a_prime, $string, $count, + $start, $factor, $multiple, $secs); + +# initialise +$seeking = 20; # how many to find +$count = 0; # how many found + +# find primes in ranges of 1000 +$secs = time; +for ($from = 1; ; $from += 1000) { + $to = $from + 999; + + # loop over all the possible factors, ie primes < sqrt($to) + for $factor (2 .. int(sqrt($to))) { + next if defined $not_a_prime[$factor]; # already known as not a prime + + # mark all the multiples of $factor as non-primes (sieve of Eratosthenes) + $start = int($from / $factor); # multiples less than $start have already been done + $start = 2 if $start < 2; + for ($multiple = $start; $factor * $multiple <= $to; $multiple ++) { + $not_a_prime[$factor * $multiple] = 1; + } + } + + # now test the primes in this range for left-truncatability + TEST: for $test ($from .. $to) { + + # remove ineligibles - not prime, is a single digit, contains 0 or ends in 9 + next if (defined $not_a_prime[$test] or $test =~ m|0| or $test =~ m|9$| or $test < 11); + + # test for left-truncatability and construct string showing proof + $this = $test; + $string = qq[$this]; + + # remove successive left digits and test the residue for primeness + while ($this =~ s|\d(\d+)|$1|) { + next TEST if $not_a_prime[$this]; + $string .= qq[ > $this]; + } + + # an answer! + say $string; + if (++ $count >= $seeking) { + say '' . (time - $secs) . qq[ seconds\n]; + exit; + } + } +} diff --git a/challenge-147/peter-campbell-smith/perl/ch-2.pl b/challenge-147/peter-campbell-smith/perl/ch-2.pl new file mode 100755 index 0000000000..e10b24053a --- /dev/null +++ b/challenge-147/peter-campbell-smith/perl/ch-2.pl @@ -0,0 +1,128 @@ +#!/usr/bin/perl + +# Peter Campbell Smith - 2022-01-10 +# PWC 147 task 2 + +use v5.28; +use warnings; +use strict; + +# Write a script to find the first pair of Pentagon Numbers whose sum and difference +# are also a Pentagon Number. Pentagon numbers can be defined as P(n) = n(3n - 1)/2. + +my $seeking = 1; +# first_method(); # see blog - it works but is slow +second_method(); # this is better + +#--- + +sub first_method { + + # first method + my ($found, $n, $pentagon, %p, @f, $m, $diff, %queue, $sum, $mm, $nn, $sum2, $start); + + $start = time; + $found = 0; + + for ($n = 1; ; $n ++) { + + # generate pentagon numbers sequentially + $pentagon = $n * (3 * $n - 1) / 2; + $p{$pentagon} = $n; # so for any $j <= $n, $j is a pentagon number if $p{$j} + $f[$n] = $pentagon; # and the $jth pentagon number is $f[$j] + next if $n == 1; + + # check the difference between this pentagon number ($n) and all smaller ones ($m) + for $m (1 .. $n - 1) { + $diff = $pentagon - $f[$m]; + next unless $p{$diff}; # difference is not a pentagon number + + # the difference is pentagonal; the sum will be more than $pentagon so put it in a queue to be checked later + $queue{sprintf('%012d', $f[$m] + $pentagon)} = [$m, $n]; # zero padded key so they sort numerically + + # test per wikipedia + $sum = $f[$m] + $pentagon; + } + + # is $pentagon in the queue of possible answers? + for $sum (sort keys %queue) { + ($mm, $nn) = @{$queue{$sum}}; + + # this queued number is the sum of 2 pentagons which differ by a pentagon, so ... an answer! + if ($sum == $pentagon) { # the queued sum is the pentagon we've just found + $diff = $f[$nn] - $f[$mm]; + $sum2 = $sum + 0; # get rid of zero padding + say qq[First method: ]; + say qq[Pentagon no $mm is $f[$mm]]; + say qq[Pentagon no $nn is $f[$nn]]; + say qq[Their sum is $sum2 which is pentagon number $n]; + say qq[Their difference is $diff which is pentagon number $p{$diff}]; + + if (++ $found == $seeking) { # we've achieved the goal + say '' . (time - $start) . qq[ seconds\n]; + return; + } + delete $queue{$sum}; + + # this queued sum of 2 pentagon numbers is less than the one we just found, + # so it isn't a pentagon number, so take it out of the queue + } elsif ($sum < $pentagon) { + delete $queue{$sum}; + + # else it's still larger than the pentagon we just found, so leave it in the queue + } else { + last; # and any others are larger still so we con;t need to look at them yet + } + } + } +} + +sub second_method { + + my ($found, $n, $i, $s, $m, $diff, $sum, %p, @f, $start); + + $found = 0; + $start = time; + + for ($n = 1; ; $n ++) { + + # find pentagon numbers sequentially + next unless ($i = is_pentagonal($n)); # so $n is the $i'th pentagon + + # so $n is pentagonal + $f[$i] = $n; # and the $i'th pentagon number is $f[$i] + $p{$n} = $i; # if n is a pentagon, it is the $p{$n}'th one + next if $n == 1; + + # check the difference and sum of this pentagon number ($n) and all smaller ones ($m) + for $m (1 .. $i - 1) { + $diff = $n - $f[$m]; + $sum = $n + $f[$m]; + + # difference is not a pentagon number + next unless $p{$diff}; + next unless $s = is_pentagonal($sum); # sum is not a pentagon number + + # result! + say qq[Second method: ]; + say qq[Pentagon no $i is $n]; + say qq[Pentagon no $m is $f[$m]]; + say qq[Their sum is $sum which is pentagon number $s]; + say qq[Their difference is $diff which is pentagon number $p{$diff}]; + if (++ $found == $seeking) { + say '' . (time - $start) . qq[ secs\n]; + return; + } + } + } +} + +sub is_pentagonal { + + # per Wikipedia + + my $test = (sqrt(24 * $_[0] + 1) + 1) / 6; + my $test1 = $test - int($test + 1e-19); + return (abs($test1) <= 1e-19) ? $test : 0; +} + diff --git a/challenge-147/roger-bell-west/blog.txt b/challenge-147/roger-bell-west/blog.txt new file mode 100644 index 0000000000..bd7837be26 --- /dev/null +++ b/challenge-147/roger-bell-west/blog.txt @@ -0,0 +1 @@ +https://blog.firedrake.org/archive/2022/01/The_Weekly_Challenge_147__Truncating_the_Pentagon.html diff --git a/challenge-147/ulrich-rieke/cpp/ch-1.cpp b/challenge-147/ulrich-rieke/cpp/ch-1.cpp new file mode 100644 index 0000000000..975ba98215 --- /dev/null +++ b/challenge-147/ulrich-rieke/cpp/ch-1.cpp @@ -0,0 +1,46 @@ +#include <iostream> +#include <string> +#include <cmath> +#include <vector> + +bool isPrime( int n ) { + if ( n == 1 ) + return false ; + if ( n == 2 ) + return true ; + int root = static_cast<int>( floor( sqrt( static_cast<double>( n ) ))) ; + for ( int i = 2 ; i < root + 1 ; i++ ) + if ( n % i == 0 ) + return false ; + return true ; +} + +bool isLeftTruncatablePrime( int n ) { + if ( ! isPrime( n ) ) + return false ; + std::string numberstring( std::to_string( n ) ) ; + auto found = numberstring.find( '0' ) ; + if ( found != std::string::npos ) + return false ; + int len = static_cast<int>(numberstring.length( ) ) ; + for ( int i = 0 ; i < len ; i++ ) { + int num = std::stoi( numberstring.substr( i ) ) ; + if ( ! isPrime( num ) ) + return false ; + } + return true ; +} + +int main( ) { + std::vector<int> leftTruncatables ; + int current = 0 ; + while ( leftTruncatables.size( ) < 20 ) { + current++ ; + if ( isLeftTruncatablePrime( current ) ) + leftTruncatables.push_back( current ) ; + } + for ( int i : leftTruncatables ) + std::cout << i << ' ' ; + std::cout << std::endl ; + return 0 ; +} diff --git a/challen |