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84 lines
2.6 KiB
Matlab
84 lines
2.6 KiB
Matlab
%ProjectEuler/Octave/Problem3.m
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%Matthew Ellison
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% Created:
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%Modified: 03-28-19
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%The largest prime factor of 600851475143
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%{
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Copyright (C) 2019 Matthew Ellison
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with this program. If not, see <https://www.gnu.org/licenses/>.
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%}
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%Setup your variables
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number = 600851475143; %The number we are trying to find the greatest prime factor of
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primeNums = []; %A list of prime numbers. Will include all prime numbers <= number
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factors = []; %For the list of factors of number
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tempNum = number; %Used to track the current value if all of the factors were taken out of number
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%Get the prime numbers up to sqrt(number). If it is not prime there must be a value <= sqrt
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primeNums = primes(sqrt(number));
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%Start the timer
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startTime = clock();
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%Setup the loop
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counter = 1;
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%Start with the lowest number and work your way up. When you reach a number > size(primeNums) you have found all of the factors
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while(counter <= size(primeNums)(2))
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%Divide the number by the next prime number in the list
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answer = (tempNum/primeNums(counter));
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%If it is a whole number add it to the factors
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if(mod(answer,1) == 0)
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factors(end + 1) = primeNums(counter);
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%Set tempNum so that it reflects number/factors
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tempNum = tempNum / primeNums(counter);
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%Keep the counter where it is in case a factor appears more than once
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%Get the new set of prime numbers
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primeNums = primes(sqrt(tempNum));
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else
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%If it was not an integer increment the counter
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++counter;
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end
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end
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%When the last number is not divisible by a prime number it must be a prime number
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factors(end + 1) = tempNum;
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%Stop the timer
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endTime = clock();
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%Print the results
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printf("The largest prime factor of 600851475143 is %d\n", max(factors))
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printf("It took %f seconds to run this algorithm\n", etime(endTime, startTime))
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%Cleanup your variables
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clear counter;
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clear tempNum;
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clear answer;
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clear number;
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clear primeNums;
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clear factors;
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clear startTime;
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clear endTime;
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clear ans;
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%{
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Results:
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The largest prime factor of 600851475143 is 6857
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It took 0.006256 seconds to run this algorithm
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%}
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