Xcode Playground showing a Swift diffing algorithm suitable for performing delta updates to a WKInterfaceTable

Diff.xcplayground

// arr1 is the current list
// arr2 is the new list
// the insert and delete callbacks will be called - pass these
// through to WKInterfaceTable to perform a delta update
func diff<T: Comparable>(arr1: Array<T>, var arr2: Array<T>, insertFunc: (index: Int, item: T) -> Void, deleteFunc: (Int) -> Void) {
    var idx1 = 0
    var idx2 = 0
    while (idx1 < arr1.count) {
        // identical items; step to next one
        if (idx2 < arr2.count && arr1[idx1] == arr2[idx2]) {
            idx1++
            idx2++
            continue
        }
        
        // try to re-sync: scan ahead to see if there's a match
        var matched = false
        
        for (var findidx = idx2; findidx < arr2.count; findidx++) {
            if (arr1[idx1] == arr2[findidx]) {
                // Found it - delete everything between y and z
                for (var delidx = idx2; delidx < findidx; delidx++) {
                    deleteFunc(idx2)
                    arr2.removeAtIndex(idx2)
                }
                matched = true
                break;
            }
        }
        
        if (matched) {
            continue
        }
        
        // didn't find a[x] in b, so add it
        insertFunc(index: idx2, item: arr1[idx1])
        
        arr2.insert(arr1[idx1], atIndex: idx2)
        idx1++
        idx2++
    }
    
    // Remove items after the end
    while (arr2.count > arr1.count) {
        deleteFunc(idx1)
        arr2.removeAtIndex(idx1)
    }
}

let newArray = [ "Two", "Four", "Five" ]
let oldArray = [ "One", "Two", "Three", "Four" ]
var outArray = oldArray

diff(newArray, oldArray,
    { (index: Int, item: String) -> Void in
        outArray.insert(item, atIndex: index)
    },
    { (index: Int) -> Void in
        outArray.removeAtIndex(index)
    }
);

outArray