在Swift中获取数组中所有可能的项目组合而没有重复的组 [英] Get all possible combination of items in array without duplicate groups in Swift

问题描述

我正在尝试在Array上创建扩展，我可以在不生成重复组的情况下获得数组的所有可能组合，包括无项目组合.

I'm trying to create an extension on Array where I can get all possible combinations of an array without generating duplicate groups, including a no item combination.

例如，对于此数组:

[1, 2, 3, 4]

应生成以下可能的组合:

The following possible combinations should be generated:

[[], [1], [2], [3], [4], [1, 2], [1, 3], [1, 4], [2, 3], [2, 4], [3, 4], [1, 2, 3], [1, 2, 4], [1, 3, 4], [2, 3, 4], [1, 2, 3, 4]]

请注意，没有一个组重复自己，即:如果有一个组[1，2]，则没有其他组:[2，1].

Please note that none of the groups repeat themselves, i.e: if there is a group [1, 2] there is no other group: [2, 1].

这是我所能获得的最接近的结果:

This is the closest I've been able to get to a result:

public extension Array {

func allPossibleCombinations() -> [[Element]] {
    var output: [[Element]] = [[]]
    for groupSize in 1...self.count {
        for (index1, item1) in self.enumerated() {
            var group = [item1]
            for (index2, item2) in self.enumerated() {
                if group.count < groupSize {
                    if index2 > index1 {
                        group.append(item2)
                        if group.count == groupSize {
                            output.append(group)
                            group = [item1]
                            continue
                        }
                    }
                } else {
                    break
                }
            }
            if group.count == groupSize {
                output.append(group)
            }
        }
    }
    return output
}

}

但是缺少分组大小为3的项目的可能组合(我只得到[1, 2, 3]和[2, 3, 4].

But it is missing possible combination of items in the group size 3 (I only get back [1, 2, 3] and [2, 3, 4].

非常感谢！

推荐答案

您也可以使用flatMap将它们组合成一行.

You can use flatMap also to combine them in one line.

extension Array {
    var combinationsWithoutRepetition: [[Element]] {
        guard !isEmpty else { return [[]] }
        return Array(self[1...]).combinationsWithoutRepetition.flatMap { [$0, [self[0]] + $0] }
    }
}
    
print([1,2,3,4].combinationsWithoutRepetition)

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