Project Euler with Julia 001-010

e001.jl

@elapsed sum(i for i=1:999 if i % 3 == 0 || i % 5 == 0) |> println
      
## FASTER SOLUTION
@time (Set(3:3:999) ∪ Set(5:5:999)) |> sum |> println

e002.jl

@time let (a, b) = (0, 1)
    s = 0
    while b <= 400_0000
        s += b % 2 == 0 ? b : 0
        a, b = b, a + b
    end
    println(s)
end

## Using Generator (FASTER!!!)
let fib = Channel() do c
        a, b = 1, 1
        while true
            put!(c, a)
            a, b = b, a+b
        end
    end
    s = 0
    while true
        f = take!(fib)
        f > 400_0000 && break
        f % 2 == 0 && (s += f)
    end
    println(s)
end
        

e003.jl

@time let b = 600851475143
    a = 2
    while b > a
        while b % a == 0
            b = div(b, a)
        end
        a += 1
    end
    println(b)
end

e004.jl

@time let ispalindrome(n) = "$n" == reverse("$n")
    (a*b for a=100:999, b=100:999 if ispalindrome(a*b)) |> maximum |> println
end

e005.jl

@time reduce(lcm, 1:20) |> println 

e006.jl

@time begin
    abs(sum(1:100)^2 - sum(i^2 for i=1:100)) |> println
end

e007.jl

function isprime(n)
    n < 2 && return false
    n in (2, 3) && return true
    (n % 2 == 0 || n % 3 == 0) && return false
    n < 8 && return true
    k = 5
    l = Int(floor(√n + .5))
    while k <= l
        (n % k == 0 || n % (k+2) == 0) && return false
        k += 6
    end
    true
end

@time let p = Channel() do c
        put!(c, 2)
        a = 3
        while true
            if isprime(a); put!(c, a); end
            a += 2
        end
    end
    Iterators.take(p, 10001) |> collect |> last |> println
end

e008.jl

@time let s = """73167176531330624919225119674426574742355349194934
96983520312774506326239578318016984801869478851843
85861560789112949495459501737958331952853208805511
12540698747158523863050715693290963295227443043557
66896648950445244523161731856403098711121722383113
62229893423380308135336276614282806444486645238749
30358907296290491560440772390713810515859307960866
70172427121883998797908792274921901699720888093776
65727333001053367881220235421809751254540594752243
52584907711670556013604839586446706324415722155397
53697817977846174064955149290862569321978468622482
83972241375657056057490261407972968652414535100474
82166370484403199890008895243450658541227588666881
16427171479924442928230863465674813919123162824586
17866458359124566529476545682848912883142607690042
24219022671055626321111109370544217506941658960408
07198403850962455444362981230987879927244284909188
84580156166097919133875499200524063689912560717606
05886116467109405077541002256983155200055935729725
71636269561882670428252483600823257530420752963450""" 

    xs = parse.(Int, (x for x in s if isdigit(x)))
    [prod(xs[i:i+4]) for i = 1:length(xs)-4] |> maximum |> println
end

e009.jl

let xs = 3:999
    result = 0
    for a in xs
        for b in (a+1):999
            c = 1000 - a - b
            result = (a^2+b^2==c^2) ? a*b*c : 0
            result > 0 && (println(result);return)
        end
    end
end

e010.jl

@time filter(isprime, 2:2e6) |> sum |> Int |> println

# 속도를 개선한 버전
@time let n = 200_0000
        s = trues(n)
        s[1] = false
        for i = (2:Int(floor(√n + 0.5)))
         if s[i]
          s[i+i:i:end] = zeros((n - i) ÷ i)
         end
        end
        sum([i for i = 1:n if s[i]]) |> println
end