Factorial with intermediate results - Swift playgrounds - index out of range error

Question

Getting blind from looking at this for too long. Can't spot the error. Getting the "index out of range" error when calling the function factorialIntermediateResults(n: 4) Hope somebody can take a look with fresh eyes and help me spot the error. Thanks!

func factorialIntermediateResults(n: Int) -> [Int] {
    if n == 0 || n == 1 { return [1] }
    var results = [Int]()
    doAllFactorials(n, &results, 0)
    return results
}

func doAllFactorials(_ n: Int, _ results: inout [Int], _ level: Int) -> Int {
    if n > 1 {
        results[level] = n * doAllFactorials(n-1, &results, level+1)
        return results[level]
    } else {
        results[level] = 1
        return 1
    }
}

factorialIntermediateResults(n: 4)

BTW - using recursion instead of a simple loop is pretty inefficient for this task. — rmaddy, Dec 02 '17 at 03:18
For factorials above 20! see: https://stackoverflow.com/a/43830823/1630618 — vacawama, Dec 02 '17 at 03:31

score 3 · Accepted Answer · answered Dec 02 '17 at 03:15

3

results is an empty array but you try to access values without appending values first.

The simplest solution might be to pre-populate your array with zeros.

var results: [Int] = Array(repeating: 0, count: n)

answered Dec 02 '17 at 03:15

rmaddy

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Yep. I was just writing that very answer. – vacawama Dec 02 '17 at 03:15

Factorial with intermediate results - Swift playgrounds - index out of range error

1 Answers1