import numpy as np

def get_matches(x, y, r):
    sorted_idx = np.argsort(y)

    y = y[sorted_idx]
    matches = []
    for i in range(x.shape[0]):
        left = np.searchsorted(y, x[i] - r, side='left')
        right = np.searchsorted(y, x[i] + r, side='right')
        matches.append(list(range(left, right)))
    return matches


if __name__ == '__main__':
    x = np.array([1, 2, 3])
    y = np.array([3, 4, 5])
    r = 2
    matches = get_matches(x, y, r)
    print(matches)