quantum/grover.py

# Full circuit + example: https://cstheory.stackexchange.com/questions/38538/oracle-construction-for-grovers-algorithm
# X-Axis control: https://algassert.com/post/1706
# http://twistedoakstudios.com/blog/Post2644_grovers-quantum-search-algorithm
import itertools
import random
from pprint import pprint


def classical_func_search_multi_rv(func, input_range):
    """Grover’s algorithm takes a function, searches through
    the implicit list of possible inputs to that function, and
    returns inputs that causes the function to return true.
    """
    rv = []
    for i, params in enumerate(input_range):
        result = func(params)
        if result:
            rv.append(params)
    return rv


def classical_func_search_single_rv(func, input_range):
    """Grover’s algorithm takes a function, searches through
    the implicit list of possible inputs to that function, and
    returns EXACTLY ONE input that causes the function to return true.
    """
    rv = None
    for i, params in enumerate(input_range):
        result = func(params)
        if result and rv is None:
            rv = result
        else:
            raise Exception("Exactly one result is needed")
    return rv


def _3sat(params):
    # 3-SAT from here: https://qiskit.org/textbook/ch-applications/satisfiability-grover.html
    x1, x2, x3 = params
    return (not x1 or not x2 or not x3) and \
           (x1 or not x2 or x3) and \
           (x1 or x2 or not x3) and \
           (x1 or not x2 or not x3) and \
           (not x1 or x2 or x3)


def _3sat_2(params):
    # 3-SAT from here: https://cstheory.stackexchange.com/questions/38538/oracle-construction-for-grovers-algorithm
    x1, x2, x3, x4 = params
    return (not x1 or not x3 or not x4) and \
           (x2 or x3 or not x4) and \
           (x1 or not x2 or x4) and \
           (x1 or x3 or x4) and \
           (not x1 or x2 or not x3)


def classical_3sat(func):
    # Generate all possible true/false tuples for the 3-sat problem
    input_range = list(itertools.product([True, False], repeat=3))
    random.shuffle(input_range)
    return classical_func_search_multi_rv(func, input_range)


def main():
    pprint(classical_3sat(_3sat))


if __name__ == "__main__":
    main()