[Solved] Swift – Group elements of Array by value (2 by 2, 3 by 3, etc…)

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Here is my version where I filter on a range based on first value of the array and the coef variable, based on the result I slice away those elements already counted and filter again on the smaller array in a loop. This solution requires the input array to be sorted in ascending order

func group(_ array: [Int], coef: Int) -> [Int: Int] {
    var result:[Int:Int] = [:]

    var start = array[0]
    var end = start + coef - 1
    var arr  = array

    while start <= array[array.count - 1] {
       let count = arr.filter({ $0 >= start && $0 <= end}).count

       result[start] = count
       start = end + 1
       end = start + coef - 1
       arr = Array(arr[count...])
    }
    return result
}

And here is a recursive version of the above function

func group(_ array: [Int], coef: Int) -> [Int: Int] {
    var result:[Int:Int] = [:]
    if array.isEmpty { return result }

    let end = array[0] + coef - 1
    let count = array.filter({ $0 >= array[0] && $0 <= end}).count
    result[array[0]] = count
    result = result.merging(group(Array(array[count...]), coef: coef)) { $1 }
    return result
}

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solved Swift – Group elements of Array by value (2 by 2, 3 by 3, etc…)