ArrayCompare.swift

//
//  ArrayCompare.swift
//
//  Created by Daniel Tartaglia on Sep 10, 2015.
//  Inspired by http://www.swift-studies.com/blog/2015/5/15/swift-coding-challenge-incremental-updates-to-views
//

public func findDifferences<T : Hashable>(old: [T], new:[T], moveBlock: (_ from: Int, _ to: Int)->()) -> (insertions: [Int], removals: [Int])
{
    var insertionIndexs = [Int]()
    var removalIndexs = [Int]()
    var newPositions = [T : Int]()
    for index in 0 ..< new.count {
        newPositions[new[index]]=index
    }
    for oldPosition in 0 ..< old.count {
        let item = old[oldPosition]
        if let newPosition = newPositions[item] {
            if oldPosition != newPosition{
                moveBlock(oldPosition, newPosition)
            }
            newPositions.removeValue(forKey: item)
        } else {
            removalIndexs.append(oldPosition)
        }
    }
    for (_, position) in newPositions {
        insertionIndexs.append(position)
    }
    return (insertions: insertionIndexs, removals: removalIndexs)
}