encoding and decoding equatable elements from Array.

Array+RunLength.swift

//
//	Array+RunLength.swift
//	ZKit
//
//	The MIT License (MIT)
//
//	Copyright (c) 2020 Electricwoods LLC, Kaz Yoshikawa.
//
//	Permission is hereby granted, free of charge, to any person obtaining a copy
//	of this software and associated documentation files (the "Software"), to deal
//	in the Software without restriction, including without limitation the rights
//	to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//	copies of the Software, and to permit persons to whom the Software is
//	furnished to do so, subject to the following conditions:
//
//	The above copyright notice and this permission notice shall be included in
//	all copies or substantial portions of the Software.
//
//	THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//	IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//	FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//	AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
//	WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//	OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
//	THE SOFTWARE.
//

//	Make Run Length Encoding
//
//	There are some cases where you like to compact number of sequnced same items over and over again.
//	This piece of code usues run length encoding to compact them, and decode them to bring back to
//	the original sequence of items.
//
//	Usage:
//		let numbers = [1, 1, 1, 2, 2, 2, 2, 3, 4, 5, 5, 5, 5]
//		let runs = numbers.makeRunLength() // [(element: 1, count: 3), (element: 2, count: 4), (element: 3, count: 1), (element: 4, count: 1), (element: 5, count: 4)]
//		let duplicated = Array(runs: runs) // [1, 1, 1, 2, 2, 2, 2, 3, 4, 5, 5, 5, 5]



extension Array where Element: Equatable {

	func makeRunLength() -> [(element: Element, count: Int)] {
		var runs = [(element: Element, count: Index)]()
		var run: (element: Element, count: Index)?
		for (index, value) in self.enumerated() {
			if run?.element == value {
				run?.count += 1
			}
			else {
				if let run = run {
					runs.append(run)
				}
				run = (element: value, count: 1)
			}
		}
		if let run = run {
			runs.append(run)
		}
		return runs
	}

	init(runs: [(element: Element, count: Int)]) {
		var elements = Array()
		for run in runs {
			elements += Array(repeating: run.element, count: run.count)
		}
		self = elements
	}

}