sorting problem

hello,im having trouble to resolve this problem. maybe someone of you knows a solution.I have a music collection composed of artists and songs.I want to listen to each song but each songs should be spread out evently so the same artist is not played twice in a row. example: if artist-1 has 10 songs and the total songs are 100, then 1 song of every 10 would be of artist-1. the order the artists are played doesnt matter.whats the formula to achive this?My collection: (12 songs total)A1 (5 songs): S1,S2,S3,S4,S5
A2 (3 songs): S1,S2,S3
A3 (3 songs): S1,S2,S3
A4 (1 songs): S1Possible result:
A1-S1
A2-S1
A1-S2
A2-S2
A1-S3
A2-S3
A1-S4
A3-S1
A1-S5
A3-S2
A4-S1
A3-S3thanks in advance