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Added solution to problem 37

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Mattrixwv
2021-07-02 00:47:23 -04:00
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commit f1e42d1f18
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Problem36.m
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function [] = Problem36()
%ProjectEuler/ProjectEulerOctave/Problem36.lua
%ProjectEuler/ProjectEulerOctave/Problem36.m
%Matthew Ellison
% Created: 06-29-21
%Modified: 06-29-21

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Problem37.m Normal file
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function [] = Problem37()
%ProjectEuler/ProjectEulerOctave/Problem37.m
%Matthew Ellison
% Created: 07-01-21
%Modified: 07-01-21
%Find the sum of the only eleven primes that are both truncatable from left to right and right to left (2, 3, 5, and 7 are not counted).
%{
Copyright (C) 2021 Matthew Ellison
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>.
%}
%Setup the variables
truncPrimes = []; %All numbers that are truncatable primes
sumOfTrunc = 0; %The sum of all elements in truncPrimes
%Start the timer
startTime = clock();
%Get all the primes up to a max number
primeList = primes(750000);
%primeList = primes(30);
for loc = 5 : size(primeList)(2)
currentPrime = primeList(loc);
isTruncPrime = true;
%Convert the prime to a string
primeString = num2str(currentPrime);
%If the string contains an even digit move to the next prime
strLoc = 1;
while((strLoc <= size(primeString)(2)) && (isTruncPrime))
ch = primeString(strLoc);
%Allow 2 to be the first digit
if((strLoc == 1) && (ch == '2'))
strLoc = strLoc;
else
if((ch == '0') || (ch == '2') || (ch == '4') || (ch == '6') || (ch == '8'))
isTruncPrime = false;
end
end
++strLoc;
end
%Start removing digits from the left and see if the number stays prime
if(isTruncPrime)
for truncLoc = 2 : size(primeString)(2)
%Create a substring of the prime, removing the needed digits frome the left
primeSubstring = substr(primeString, truncLoc);
%Convert the string to an int and see if the number is still prime
newPrime = str2num(primeSubstring);
if(~isprime(newPrime))
isTruncPrime = false;
break;
end
end
end
%Start removing digits from the right and see if the number stays prime
if(isTruncPrime)
for truncLoc = 1 : size(primeString)(2) - 1
%Create a substring of the prime, removing the needed digits from the right
primeSubstring = substr(primeString, 1, size(primeString)(2) - truncLoc);
%Convert the string to an int and see if the number is still a prime
newPrime = str2num(primeSubstring);
if(~isprime(newPrime))
isTruncPrime = false;
break;
end
end
end
%If the number remained prime through all operations add it to the table
if(isTruncPrime)
truncPrimes(end + 1) = currentPrime;
end
%End the loop if we have collected enough primes
if(size(truncPrimes)(2) == 11)
break;
end
end
%Get the sum of all elements in the truncPrimes vector
sumOfTrunc = sum(truncPrimes);
%Stop the timer
endTime = clock();
%print the results
printf("The sum of all left and right truncatable primes is %d\n", sumOfTrunc);
printf("It took %f seconds to run this algorithm\n", etime(endTime, startTime))
end
%{
The sum of all left and right truncatable primes is 748317
It took 38.635521 seconds to run this algorithm
%}