B3: Less Than Oracle I

Problem Statement

You are given integers $n$ and $L$. Implement the oracle $O$ on a quantum circuit $\mathrm{qc}$ with $n$ qubits, which multiplies all the probability amplitudes $a_i$ of $\ket{0},\ \ket{1},\ ...\ \ket{L-1}$ by $-1$.

Constraints

• $1 \leq n \leq 5$
• $1 \leq L \leq 2^n$
• Global phase is ignored in judge.
• Integers must be encoded by little-endian notation, i.e., $\ket{100} = 1 \neq \ket{001}$.
• The submitted code must follow the specified format:

from qiskit import QuantumCircuit
 
 
def solve(n: int, L: int) -> QuantumCircuit:
    qc = QuantumCircuit(n)
    # Write your code here:
 
    return qc

Sample Input

• $n = 2,\ L=3$: The implemented oracle $O$ should perform the following transformation.

Hints

from qiskit.circuit.library import Gate
 
qc.append(Gate().control(n - 1), range(n))