The question imply that Andy and Doris both prefer restaurant on the left of list. Our goal is to find the common interesting that is most preferred by them.
["Shogun", "Tapioca Express", "Burger King", "KFC"]
["KFC", "Shogun", "Burger King"]
So we can compute the sum of index as key and a list of restaurants as value;
If the sum of index is smaller means they are preferred by Andy and Doris.