54 lines
1 KiB
Julia
54 lines
1 KiB
Julia
const cache = Dict{BigInt, Tuple{Bool, BigInt}}()
|
|
|
|
Base.reverse(n::Integer) = parse(BigInt, string(n) |> reverse)
|
|
function lychrel(n::BigInt)::Tuple{Bool, BigInt}
|
|
if haskey(cache, n)
|
|
return cache[n]
|
|
end
|
|
|
|
r = reverse(n)
|
|
rst = (true, n)
|
|
seen = Set{BigInt}()
|
|
for i in 0:500
|
|
n += r
|
|
r = reverse(n)
|
|
if n == r
|
|
rst = (false, big(0))
|
|
break
|
|
end
|
|
if haskey(cache, n)
|
|
rst = cache[n]
|
|
break
|
|
end
|
|
push!(seen, n)
|
|
end
|
|
|
|
for bi in seen
|
|
cache[bi] = rst
|
|
end
|
|
return rst
|
|
end
|
|
|
|
seeds = BigInt[]
|
|
related = BigInt[]
|
|
palin = BigInt[]
|
|
|
|
for n in big.(1:10000)
|
|
t = lychrel(n)
|
|
if ! t[1]
|
|
continue
|
|
end
|
|
if n == t[2]
|
|
push!(seeds, n)
|
|
else
|
|
push!(related, n)
|
|
end
|
|
|
|
if n == t[2]
|
|
push!(palin, t[2])
|
|
end
|
|
end
|
|
|
|
println(length(seeds), " lychrel seeds: ", join(seeds, ", "))
|
|
println(length(related), " lychrel related")
|
|
println(length(palin), " lychrel palindromes: ", join(palin, ", "))
|