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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _vertex_one_color_qubo(x_vars):
 """For each vertex, it should have exactly one color. Generates the QUBO to enforce this constraint. Notes ----- Does not enforce neighboring vertices having different colors. Ground energy is -1 * |G|, infeasible gap is 1. """

    Q = {}
    for v in x_vars:
        for color in x_vars[v]:
            idx = x_vars[v][color]
            Q[(idx, idx)] = -1

        for color0, color1 in itertools.combinations(x_vars[v], 2):
            idx0 = x_vars[v][color0]
            idx1 = x_vars[v][color1]

            Q[(idx0, idx1)] = 2

    return Q