Populate `payoff_array` with the payoff values for player 1 in the
    tournament game.

    Parameters
    ----------
    payoff_array : ndarray(float, ndim=2)
        ndarray of shape (m, n), where m = n choose k, prefilled with
        zeros. Modified in place.
    k : scalar(int)
        Size of the subsets of nodes.

def _populate_tournament_payoff_array1(payoff_array, k):
    """
    Populate `payoff_array` with the payoff values for player 1 in the
    tournament game.

    Parameters
    ----------
    payoff_array : ndarray(float, ndim=2)
        ndarray of shape (m, n), where m = n choose k, prefilled with
        zeros. Modified in place.
    k : scalar(int)
        Size of the subsets of nodes.

    """
    m = payoff_array.shape[0]
    X = np.arange(k)
    for j in range(m):
        for i in range(k):
            payoff_array[j, X[i]] = 1
        X = next_k_array(X)