15. Caterpillar method. AbsDistinct.swift

import Foundation
import Glibc

// Solution @ Sergey Leschev, Belarusian State University

// 15. Caterpillar method. AbsDistinct.

// A non-empty array A consisting of N numbers is given. The array is sorted in non-decreasing order. The absolute distinct count of this array is the number of distinct absolute values among the elements of the array.

// For example, consider array A such that:
//   A[0] = -5
//   A[1] = -3
//   A[2] = -1
//   A[3] =  0
//   A[4] =  3
//   A[5] =  6
// The absolute distinct count of this array is 5, because there are 5 distinct absolute values among the elements of this array, namely 0, 1, 3, 5 and 6.

// Write a function:
// class Solution { public int solution(int[] A); }
// that, given a non-empty array A consisting of N numbers, returns absolute distinct count of array A.

// For example, given array A such that:
//   A[0] = -5
//   A[1] = -3
//   A[2] = -1
//   A[3] =  0
//   A[4] =  3
//   A[5] =  6
// the function should return 5, as explained above.

// Write an efficient algorithm for the following assumptions:
// N is an integer within the range [1..100,000];
// each element of array A is an integer within the range [-2,147,483,648..2,147,483,647];
// array A is sorted in non-decreasing order.

public func solution(_ A: inout [Int]) -> Int {
    var distincts = Set<Int>()
    A.forEach { distincts.insert(abs($0)) }
    return distincts.count
}