Getting the following error when attempting this in Swift. Says all tests have passed but doesn't accept it as a solution

STDERR:
0 swift 0x00000000034bf568 llvm::sys::PrintStackTrace(llvm::raw_ostream&) + 40
1 swift 0x00000000034c0146
2 libpthread.so.0 0x00007f6e2d68c330
3 libpthread.so.0 0x00007f6e2d9ff707
4 libpthread.so.0 0x00007f6e2da01031
5 libpthread.so.0 0x00007f6e2da021fa
6 libpthread.so.0 0x00007f6e2da0091b
7 libpthread.so.0 0x00007f6e2da022a5
8 libXCTest.so 0x00007f6e28a21641
9 libXCTest.so 0x00007f6e28a40460
10 libXCTest.so 0x00007f6e28a3d5c5
11 libXCTest.so 0x00007f6e28a3f806
12 libXCTest.so 0x00007f6e28a279e0
13 libXCTest.so 0x00007f6e28a215c5 TF6XCTest14XCTAssertEqualuRxs9EquatablerFTKzT_xKzT_xKT_SS4fileVs12StaticString4lineSu_T + 101
14 libXCTest.so 0x00007f6e2da00f79 TF6XCTest14XCTAssertEqualuRxs9EquatablerFTKzT_xKzT_xKT_SS4fileVs12StaticString4lineSu_T + 83753497
15 libXCTest.so 0x00007f6e2da02e90 TF6XCTest14XCTAssertEqualuRxs9EquatablerFTKzT_xKzT_xKT_SS4fileVs12StaticString4lineSu_T + 83761456
16 libXCTest.so 0x00007f6e2da0043e TF6XCTest14XCTAssertEqualuRxs9EquatablerFTKzT_xKzT_xKT_SS4fileVs12StaticString4lineSu_T + 83750622
17 libXCTest.so 0x00007f6e2da02fb5 TF6XCTest14XCTAssertEqualuRxs9EquatablerFTKzT_xKzT_xKT_SS4fileVs12StaticString4lineSu_T + 83761749
18 libXCTest.so 0x00007f6e28a546ab
19 libXCTest.so 0x00007f6e28a2b1a2
20 libXCTest.so 0x00007f6e28a54660
21 libXCTest.so 0x00007f6e28a543e0
22 libXCTest.so 0x00007f6e28a2a280 TFC6XCTest10XCTestCase10invokeTestfT_T + 112
23 libXCTest.so 0x00007f6e28a42219 TTSf4g_n___TFC6XCTest10XCTestCase7performfCS_9XCTestRunT + 313
24 libXCTest.so 0x00007f6e28a2a14e TFC6XCTest10XCTestCase7performfCS_9XCTestRunT + 14
25 libXCTest.so 0x00007f6e28a29f45 TFC6XCTest6XCTest3runfT_T + 629
26 libXCTest.so 0x00007f6e28a42ee5 TTSf4g_n___TFC6XCTest11XCTestSuite7performfCS_9XCTestRunT + 789
27 libXCTest.so 0x00007f6e28a433b3 TTSf4g_n___TFC6XCTest11XCTestSuite7performfCS_9XCTestRunT + 2019
28 libXCTest.so 0x00007f6e28a433b3 TTSf4g_n___TFC6XCTest11XCTestSuite7performfCS_9XCTestRunT + 2019
29 libXCTest.so 0x00007f6e28a2f6db _TF6XCTest7XCTMainFGSaT13testCaseClassMCS_10XCTestCase8allTestsGSaTSSFzS0_T_____Os5Never + 4283
30 libXCTest.so 0x00007f6e2d9ff0e9 _TF6XCTest7XCTMainFGSaT13testCaseClassMCS_10XCTestCase8allTestsGSaTSSFzS0_T_____Os5Never + 83692233
31 swift 0x0000000000c795f2 llvm::MCJIT::runFunction(llvm::Function*, llvm::ArrayRef) + 1042
32 swift 0x0000000000c7d0ff llvm::ExecutionEngine::runFunctionAsMain(llvm::Function*, std::vector > const&, char const* const*) + 1215
33 swift 0x000000000083ca6f swift::RunImmediately(swift::CompilerInstance&, std::vector > const&, swift::IRGenOptions&, swift::SILOptions const&) + 2303
34 swift 0x00000000008364f8
35 swift 0x0000000000831377 swift::performFrontend(llvm::ArrayRef, char const*, void*, swift::FrontendObserver*) + 2551
36 swift 0x00000000007f8788 main + 3016
37 libc.so.6 0x00007f6e2be35f45 __libc_start_main + 245
38 swift 0x00000000007f5e56
Stack dump:
0. Program arguments: /swift-vol/swift-gen/usr/bin/swift -frontend -interpret /tmp/swift117011-18-1bsoqew.jysvhrggb9/solution.swift -target x86_64-unknown-linux-gnu -disable-objc-interop -module-name solution