├── README.md
├── 1.rb
├── 6.rb
├── 2.rb
├── 4.rb
├── 5.rb
└── 8.rb


/README.md:
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1 | Project Euler Solutions
2 | ===
3 | 
4 | Solutions to some of the problems at [Project Euler](http://projecteuler.net/).
5 | 


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/1.rb:
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 1 | #Problem 1
 2 | #Find sum of all multiples of 3 or 5 below 1000.
 3 | 
 4 | sum = 0
 5 | (1...1000).each do |x|
 6 |   if x % 3 == 0 || x % 5 == 0
 7 |     sum += x
 8 |   end
 9 | end
10 | puts sum
11 | 


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/6.rb:
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 1 | sumsquares = 0
 2 | squaresums = 0
 3 | 
 4 | (1..100).each do |x|
 5 |     sumsquares += x**2
 6 |     squaresums +=x
 7 | end
 8 | 
 9 | squaresums = squaresums ** 2
10 | 
11 | puts (squaresums - sumsquares)
12 | 


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/2.rb:
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 1 | # find sum of the even-valued terms of fibonacci terms up to 4,000,000
 2 | # 1 , 2, 3, 5, 8, 13, 21, 34, 55, ...
 3 | #
 4 | 
 5 | 
 6 | def fib(sum, curr, prev)
 7 |    if curr > 4_000_000
 8 |      puts sum
 9 |      return
10 |   end
11 |   if curr % 2 == 0
12 |     sum += curr
13 |   end
14 |   fib(sum, prev + curr, curr)
15 | end
16 | 
17 | fib(0,1,1)
18 | 
19 | 


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/4.rb:
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 1 | #finds largest palindrome made
 2 | #from two 3-digit numbers
 3 | 
 4 | 
 5 | def palindrome?(x, y)
 6 |     return true if (x*y).to_s == (x*y).to_s.reverse
 7 |     return false
 8 | end
 9 | 
10 | max = 0
11 | 100.upto(999) do |x|
12 |     100.upto(999) do |y|
13 |         max = x * y if palindrome?(x,y) and x * y > max
14 |     end
15 | end
16 | 
17 | puts max
18 | 


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/5.rb:
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 1 | #smallest positive int divisible
 2 | #by all numbers 1..20
 3 | 
 4 | def divisible?(x, lo, hi)
 5 |     (lo..hi).each do |n|
 6 |         return false if x % n != 0
 7 |     end
 8 |     return true
 9 | end
10 | 
11 | 
12 | ret = 0
13 | curr = 19
14 | 
15 | while ret == 0 do
16 |     ret = curr if divisible?(curr, 1, 20)
17 |     curr += 19
18 | end
19 | 
20 | puts ret
21 | 


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/8.rb:
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 1 | bignum = "7316717653133062491922511967442657474235534919493496983520312774506326239578318016984801869478851843858615607891129494954595017379583319528532088055111254069874715852386305071569329096329522744304355766896648950445244523161731856403098711121722383113622298934233803081353362766142828064444866452387493035890729629049156044077239071381051585930796086670172427121883998797908792274921901699720888093776657273330010533678812202354218097512545405947522435258490771167055601360483958644670632441572215539753697817977846174064955149290862569321978468622482839722413756570560574902614079729686524145351004748216637048440319989000889524345065854122758866688116427171479924442928230863465674813919123162824586178664583591245665294765456828489128831426076900422421902267105562632111110937054421750694165896040807198403850962455444362981230987879927244284909188845801561660979191338754992005240636899125607176060588611646710940507754100225698315520005593572972571636269561882670428252483600823257530420752963450"
 2 | 
 3 | lo = 0
 4 | hi = 4
 5 | max = 0
 6 | 
 7 | while hi < 999 do
 8 |     prod = 1
 9 |     (lo..hi).each do |x|
10 |         prod = prod * bignum[x].to_i
11 |     end
12 |     max = prod if prod > max
13 |     lo += 1
14 |     hi += 1
15 | end
16 | 
17 | puts max
18 | 


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