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Solution for the Collatz Challenge #3

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Solution for the Collatz Challenge #3

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bee0fec
Solution for the Collatz Challenge
phelgo Jan 25, 2016
e33d5f6
Remove redundant return
phelgo Jan 26, 2016
78b4c0f
Use proper division instead of bitwise shift on collatzCycles
phelgo Jan 26, 2016
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14 changes: 9 additions & 5 deletions Challenges/0001-The_3n+1_problem/The3n+1.playground/Contents.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -20,11 +20,15 @@ Output the maximum cycle length found in the range defined by the input values i

func challenge_0001(i: Int, _ j: Int) -> Int {

<#Write here your solution#>
func collatzCycles(n: Int) -> Int {
if n == 1 { return 1 }
return n%2==0 ? 1 + collatzCycles(n/2) : 1 + collatzCycles(3*n+1)
}

return (i...j).map(collatzCycles).maxElement()!
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@dcordero dcordero Jan 26, 2016

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Lovely maxElement I didn't know it. 🌟

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@phelgo phelgo Jan 26, 2016

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I'm not extremely fond of that ! at the end, but its quite handy

}

//assert(challenge_0001(1, 10) == 20)
//assert(challenge_0001(100, 200) == 125)
//assert(challenge_0001(201, 210) == 89)
//assert(challenge_0001(900, 1000) == 174)
assert(challenge_0001(1, 10) == 20)
assert(challenge_0001(100, 200) == 125)
assert(challenge_0001(201, 210) == 89)
assert(challenge_0001(900, 1000) == 174)
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@dcordero dcordero Jan 26, 2016

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Nice solution, I think you could simplify the collatzCycles function removing the else clausure because the if always results in a return.

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@dcordero dcordero Jan 26, 2016

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I also find more readable n/2 than n>>1 The compilers are clever enough these days to apply this type of optimisations.

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@phelgo phelgo Jan 26, 2016

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Good point, looks easier on the eyes without that else

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@phelgo phelgo Jan 26, 2016

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I was just having fun here 😄 (But I'm not entirely sure if that division is optimized btw, I recall some time ago confirming that * 0.5 was faster than / 2.0 for Floats)