Compare two sequences, report back the common elements, plus deletes/inserts required to make the sequences match

SequenceDiff.swift

// See how to use it at the bottom of this file

// Helper struct for sequenceDiff
public struct SequenceDiff<T1, T2> {
    public let common: [(T1, T2)]
    public let removed: [T1]
    public let inserted: [T2]
    public init(common: [(T1, T2)] = [], removed: [T1] = [], inserted: [T2] = []) {
        self.common = common
        self.removed = removed
        self.inserted = inserted
    }
}

public func sequenceDiff<T1, T2>(_ first: [T1], _ second: [T2], with compare: (T1,T2) -> Bool) -> SequenceDiff<T1, T2> {
    let combinations = first.flatMap { firstElement in (firstElement, second.first { secondElement in compare(firstElement, secondElement) }) }
    let common = combinations.filter { $0.1 != nil }.flatMap { ($0.0, $0.1!) }
    let removed = combinations.filter { $0.1 == nil }.flatMap { ($0.0) }
    let inserted = second.filter { secondElement in !common.contains { compare($0.0, secondElement) } }
    
    return SequenceDiff(common: common, removed: removed, inserted: inserted)
}

// How to use it:

let array1 = ["a", "b", "c"]
let array2 = ["b", "c", "d", "e"]

let diffs = sequenceDiff(array1, array2, with: ==)

print("common: \(diffs.common)")
print("removed: \(diffs.removed)")
print("inserted: \(diffs.inserted)")

// The output is
//
// common: [("b", "b"), ("c", "c")]
// removed: ["a"]
// inserted: ["d", "e"]