def _choose_single_swap(
        cls,
        mm: mapping_manager.MappingManager,
        two_qubit_ops_ints: Sequence[Sequence[QidIntPair]],
        timestep: int,
        lookahead_radius: int,
    ) -> tuple[QidIntPair, ...] | None:
        """Computes cost function with list of single candidate swaps."""
        sigma: list[tuple[QidIntPair, ...]] = [
            (swap,) for swap in cls._initial_candidate_swaps(mm, two_qubit_ops_ints[timestep])
        ]
        return cls._choose_optimal_swap(mm, two_qubit_ops_ints, timestep, lookahead_radius, sigma)
Computes cost function with list of single candidate swaps.
cirq-core/cirq/transformers/routing/route_circuit_cqc.py