Printing out all the combinations of a string

Question

iOS 11, Swift 4.0

Trying to write a recursive function to show all the possible combinations of a string. I got this, but its not quite right since I get only 20 pa

Answer 1

Not a direct answer to your question but you can get all permutations (translated from java to Swift) as follow:

public extension RangeReplaceableCollection {
    func permutations() -> [SubSequence] {
        isEmpty ? [] : permutate(.init())
    }
    private func permutate(_ subSequence: SubSequence) -> [SubSequence] {
        var permutations = isEmpty ? [subSequence] : []
        indices.forEach {
            permutations += (self[..<$0] + self[$0...].dropFirst())
                .permutate(subSequence + CollectionOfOne(self[$0]))
        }
        return permutations
    }
}

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let str = "ABCD"
print(str.permutations())   // "["ABCD", "ABDC", "ACBD", "ACDB", "ADBC", "ADCB", "BACD", "BADC", "BCAD", "BCDA", "BDAC", "BDCA", "CABD", "CADB", "CBAD", "CBDA", "CDAB", "CDBA", "DABC", "DACB", "DBAC", "DBCA", "DCAB", "DCBA"]\n"

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Per-mutating a substring

print("ABCD".dropLast().permutations())   // ["ABC", "ACB", "BAC", "BCA", "CAB", "CBA"]\n"