http://discrete.openmathbooks.org/dmoi2/section-27.html
This covers of basics of generating function
And for Recurrence relation
https://www.tutorialspoint.com/discrete_mathematics/discrete_mathematics_recurrence_relation.htm
These videos are also quite useful for understanding the basica
https://youtu.be/Pp4PWCPzeQs
https://www.youtube.com/watch?v=dUJ63nwx6Ew
https://www.youtube.com/watch?v=4_pj7aeDhSU&feature=youtu.be
YOU WILL GET SOLUTIONS OF ALMOST ALL QUESTIONS FROM KENNETH H ROSSEN SOON ON THIS CHANNEL
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