Finds the largest ascending subset and their indices contained in an Array<Int>

Subset.swift

import Foundation

typealias IndexedSlice = (slice: ArraySlice<Int>, index: Int)
let ascending: (Int, Int) -> Bool = { $0 < $1 }

func solution(input: [Int]) -> [Int] {
	assert(input.count > 0, "Cannot calculate for empty array")
	return largestAscendingSlicesWithIndex(input).map { $0.index }
}

func largestAscendingSlicesWithIndex(array: [Int]) -> [IndexedSlice] {
	var result = [IndexedSlice]()
	var longestSlice = array.largestSliceCount(ascending)
	for var idx = 0; idx <= array.count - longestSlice; idx++ {
		let slice = array[idx..<idx + longestSlice]
		if slice.isSorted(ascending) {
			result.append((slice, idx))
		}
	}
	return result
}

// MARK: - Extensions / Helper

extension Array {
	func largestSliceCount(@noescape predicate: (T, T) -> Bool) -> Int {
		var (largestCount, currentCount) = (1, 1)
		for i in 1..<count {
			if predicate(self[i-1], self[i]) {
				if ++currentCount >= largestCount  {
					largestCount = currentCount
				}
			} else {
				currentCount = 1
			}
		}
		return largestCount
	}
}

extension ArraySlice {
	func isSorted(@noescape isOrderedBefore: (T, T) -> Bool) -> Bool {
		for i in 1..<count {
			if !isOrderedBefore(self[i-1], self[i]) {
				return false
			}
		}
		return true
	}
}