Appending an int key in a dictionary

Question

I am trying to create a dictionary from the following lists:

link_i = [1, 1, 3, 3, 3, 4, 4, 5, 5, 6]
link_j = [2, 3, 1, 2, 5, 5, 6, 6, 4, 4]

link_i = [1, 1,