How to control frequency of occurence of given element with another element or in the given spot?

Question

Let\'s say I have two lists:

char_list = [\'a\',\'b\',\'c\',\'d\',\'e\',\'f\',\'g\',\'h\',\'i\',\'j\',\'k\',\'l\']
n_list = [3,2,1,2,1,3]

and wan