1115. Print FooBar Alternately (Swift version)

main.swift

//
// The problem repeats the LC problem '1115. Print FooBar Alternately'
// https://leetcode.com/problems/print-in-order

// Implement your solution inside the `FooBar` class.
// Test with: swift main.swift

final class FooBar: Sendable {
    let n: Int

    init(_ n: Int) {
        self.n = n
    }

    func foo(_ printFoo: @escaping @Sendable () async -> Void) async {
        for _ in 0..<n {
            await printFoo()  // Don't change this line
        }
    }

    func bar(_ printBar: @escaping @Sendable () async -> Void) async {
        for _ in 0..<n {
            await printBar()  // Don't change this line
        }
    }
}

// MARK: -
// This section is required for the problem testing.
// Do not modify.
let expected =
    "foobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobarfoobar"

for _ in 0..<10_000 {
    await runSolution()
}

func runSolution() async {
    actor Context {
        var str = ""
        func append(_ suffix: String) {
            str += suffix
        }
    }

    let result = await withTaskGroup(of: Void.self) { group in
        let fb = FooBar(100)
        let result = Context()
        group.addTask {
            await fb.bar {
                await result.append("bar")
            }
        }
        group.addTask {
            await fb.foo {
                await result.append("foo")
            }
        }
        await group.waitForAll()
        return await result.str
    }

    assert(result == expected, "Wrong string:\n\(result)\nExpected string:\n\(expected)")
}