Put the digits 1-3 (later 1-4 and 1-5) once each in the white circles and once each in the shaded circles. When 3 circles are adjacent in a straight line, the middle circle should contain the difference of the numbers in the other two circles. Some of the circles are already filled for you.

A. | B. | C. | D. |

E. | F. | G. | H. |

I. | J. | K. | L. |

M. | N. | O. | P. |

Q. | R. | S. |

The answers are here.