Contents.swift

import Foundation

public func solution(_ A : inout [Int]) -> Int {

    let N = A.count
    
    let sortedValues = A.sorted(by: { $0 < $1 })
    
    let maxTriplet1 = sortedValues[0] * sortedValues[1] * sortedValues[N-1]
    let maxTriplet2 = sortedValues[N-1] * sortedValues[N-2] * sortedValues[N-3]
    
    return max(maxTriplet1, maxTriplet2)
    
}

var A = [-5, 5, -5, 4]

print(solution(&A))

// MARK: - Prompt

/*
 A non-empty array A consisting of N integers is given. The product of triplet (P, Q, R) equates to A[P] * A[Q] * A[R] (0 ≤ P < Q < R < N).

 For example, array A such that:

   A[0] = -3
   A[1] = 1
   A[2] = 2
   A[3] = -2
   A[4] = 5
   A[5] = 6
 contains the following example triplets:

 (0, 1, 2), product is −3 * 1 * 2 = −6
 (1, 2, 4), product is 1 * 2 * 5 = 10
 (2, 4, 5), product is 2 * 5 * 6 = 60
 Your goal is to find the maximal product of any triplet.

 Write a function:

 public func solution(_ A : inout [Int]) -> Int

 that, given a non-empty array A, returns the value of the maximal product of any triplet.

 For example, given array A such that:

   A[0] = -3
   A[1] = 1
   A[2] = 2
   A[3] = -2
   A[4] = 5
   A[5] = 6
 the function should return 60, as the product of triplet (2, 4, 5) is maximal.

 Write an efficient algorithm for the following assumptions:

 N is an integer within the range [3..100,000];
 each element of array A is an integer within the range [−1,000..1,000].
*/