Lets there are n stores.
A customer order x items. All the stores might not have all the items from the order.
So find the store/combination of stores that can serve the order request such that the combination that contain least number of stores.
Edit:
Example: Lets say there are 4 stores. User is ordering item 1, 3, 6, 7
Store 1 sells item 1, item 6 Store 2 sells item 1, item 2, item 3, item 4, item 5 Store 3 sells item 6, 7, 8, 9, 10 Store 4 sells item 5, item 7
The combinations of stores that can fulfil the orders { 2, 3 } , { 1, 2, 4}
So optimal solution in this case is {2,3}
P.S: I was asked this question in an interview. What would be the algorithm that would fit into the problem?