# Solutions for Problem 73

NOTE: Another easter egg for the next person who solves it (no links/updates on the main page).

How many fractions are there of the form n/d (where n and d are positive integers with no common divisors) between 1/3 and 1/2 for d < 12001?

Note: Limit was increased lately from 10,000 to 12,000. (Thomas's won't work now, or will at least need it's limit adjusted)

Runtime: unknown

```{- Return all the fractions i in the range 1/3 < i < 1/2 for some divisor "n"
- Note: results are sorted by default. -}
fracs :: Double -> [Double]
fracs n = map (\x -> x/n) (takeWhile (< n/2) (dropWhile (<= n/3) [1..]))

{- Combine two sorted lists of doubles (can also use type: Eq a => [a] -> [a] -> [a])
- returning a sorted single list without duplicates. -}
comb :: [Double] -> [Double] -> [Double]
comb [] ys = ys
comb xs [] = xs
comb (x:xs) (y:ys) | x == y = [x] ++ (comb xs ys)
comb (x:xs) (y:ys) | x > y = [y] ++ (comb (x:xs) ys)
comb (x:xs) (y:ys) = [x] ++ (comb xs (y:ys))

{- Combine all the lists together for divisor 5..10000 and print the length -}
main = print (length (foldl (\l n -> comb l (fracs n)) [] [5..10000]))
```

This is a slow brute force approach, can be done a lot faster!

## Pyhton by Althalus

Runtime: 496.6 seconds. Horrible.

```third = 1.0/3
half = 1.0/2
fractions = {}
for d in range(1,12001):
if d % 100 == 0: print d
for n in range(1,d):
tmp = float(n)/d
if tmp > third and tmp < half:
f = gcd(n,d)
fractions[(n/f,d/f)] = 1
print len(fractions.keys())
```