bernstein.py

from qiskit import QuantumRegister, QuantumCircuit, ClassicalRegister, Aer, execute
from qiskit.visualization import plot_histogram

DIGITS = 3

def oracle(secret, as_gate=True):
    o_qc = QuantumCircuit(DIGITS+1)
    
    for i in range(DIGITS):
        if secret[::-1][i] == '1':
            o_qc.cx(i,DIGITS)
        else:
            o_qc.i(i)

    return o_qc.to_gate(label="oracle") if as_gate else o_qc
  
 
cr = ClassicalRegister(DIGITS, "cr")
qr = QuantumRegister(DIGITS, "digits")
aux = QuantumRegister(1, "aux")
qc = QuantumCircuit(qr, aux, cr)

qc.h(qr)

qc.x(aux)
qc.h(aux)

qc.append(oracle('111'), [*qr, *aux])

qc.h(qr)

qc.measure(qr, cr)

results = execute(qc,Aer.get_backend('qasm_simulator'), shots=1000).result().get_counts()
plot_histogram(results)