Euler Problem 3 Python Solution
The problem is to find the largest prime factor of 600851475143.
Some ugly python and an ugly solution. Clearly not very computationally efficient as I’m recalculating primes each time. There are also other computationally more efficient solutions out there in any case. This is just here for my reference:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 | import mathdef getprimes(input): i = input #math.sqrt(input) vals = range(2,int(i)) for n in vals: for j in xrange(n+n,int(i),n): if j in vals: vals.remove(j) vals.reverse() return valsinput = 600851475143Lprimes_max = 100while 1: primes = getprimes(primes_max) #print primes p = 0 for i in primes: if input%i == 0: print "factor: ",i input = input/i p = 1 if primes_max > math.sqrt(input): if p == 0: print "factor: ",input break primes_max = primes_max + 1000 print primes_max |
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[…] first I attempted to solve this using the sieve code I wrote for problem 3. However that code used Python lists and was removing elements as it progressed. That was horribly […]