Naive 8Queens puzzle solution with bitmasks

8Queens.swift

func queen(atFile file: Int, rank: Int) -> UInt64 {
    0b00000001_00000001_00000001_00000001_00000001_00000001_00000001_00000001 << (file) |
    0b00000000_00000000_00000000_00000000_00000000_00000000_00000000_11111111 << (rank * 8) |
    0b10000000_01000000_00100000_00010000_00001000_00000100_00000010_00000001 >> ((file - rank) * 8) |
    0b00000001_00000010_00000100_00001000_00010000_00100000_01000000_10000000 >> ((7 - file - rank) * 8)
}

func occupiedIndices(in board: UInt64) -> some Sequence<(file: Int, rank: Int)> {
    sequence(state: (board, 0)) { state in
        let offset = state.0.trailingZeroBitCount
        state.1 += offset
        state.0 >>= offset + 1
        defer { state.1 += 1 }
        guard state.1 < MemoryLayout<UInt64>.size * 8 else { return nil }
        return (file: state.1 % 8, rank: state.1 / 8)
    }
}

func traverse(_ board: UInt64 = 0, mask: UInt64 = 0, results: inout Set<UInt64>) {
    if board.nonzeroBitCount == 8 {
        results.insert(board)
    } else {
        for (file, rank) in occupiedIndices(in: ~mask) {
            let queen = queen(atFile: file, rank: rank)
            guard board & queen == 0 else { continue }
            traverse(board | (1 << (rank * 8 + file)), mask: mask | queen, results: &results)
        }
    }
}

var results: Set<UInt64> = []
traverse(results: &results)

for result in results {
    print(occupiedIndices(in: result).map {
        "\(Character(UnicodeScalar($0 + 97)!))\(Character(UnicodeScalar($1 + 49)!))"
    }.joined(separator: ", "))
}