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   "source": [
    "# Example 3: Two-qubit equality circuit\n",
    "Create a circuit that checks whether two qubits are equal in the computational basis. "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "from qiskit import QuantumRegister, ClassicalRegister, QuantumCircuit\n",
    "from qiskit import Aer, execute\n",
    "from qiskit.tools.visualization import plot_histogram"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Create a 2-qubit input register and a 1-qubit output register\n",
    "# Create a 1-bit classical register for the measurement`\n",
    "# Create a circuit (qc) including those registers\n",
    "\n",
    "qin = QuantumRegister(2)  # input\n",
    "qout = QuantumRegister(1) # output\n",
    "c = ClassicalRegister(1)\n",
    "qc = QuantumCircuit(qin,qout,c)\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Define a python function that takes a circuit, an input register, and an output register\n",
    "# The function adds gates to the circuit to implement the equals circuit\n",
    "\n",
    "def equal2(circ, input, output) :\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Build a circuit that initializes the input bits to |0> or |1> (using an X gate)\n",
    "# Calls the equal2 function and then measures the output\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "qc.draw(output='mpl')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Simulate and show results\n",
    "backend = Aer.get_backend('qasm_simulator')\n",
    "job = execute(qc, backend, shots=512)  # shots default = 1024\n",
    "result = job.result()\n",
    "print(result.get_counts())\n",
    "plot_histogram(result.get_counts())"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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