Project-Euler
Ruby

# Largest Prime Factor

# What is Project Euler

Project Euler is a website with a collection of programming and mathematical problems. Each challenge varies in difficulty and there are over 600 challenges. I highly recommend anyone interested in puzzles and programming to create an account and start solving. About Project Euler

** Stop here if you have not yet tried and solved Problem 3. **

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# Problem 3

The prime factors of 13195 are 5, 7, 13 and 29.

What is the largest prime factor of the number 600851475143 ?

```
class Problem3
require 'benchmark'
def question
"The prime factors of 13195 are 5, 7, 13 and 29.
What is the largest prime factor of the number 600851475143 ?"
end
def largest_prime_factor n
max = 0
limit = n
runner = 2
while(runner <= limit) do
factor = 0
if limit % runner == 0
limit = limit / runner
factor = runner
max = factor if factor > max
else
runner = runner + 1
end
end
max
end
def solve
largest_prime_factor(600851475143)
end
def benchmark
Benchmark.measure { solve }
end
def correct?
solve === answer
end
private
def answer
6857
end
end
```

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