My wife goes to the super market while I first go to the bank. When I later go to the super market to find her, I can not.
The super market has aisles laid out in a grid with three columns and twelve rows. I enter the super market in the lower right corner. She is moving in a random fashion, three times slower than me.
What is my best strategy for finding her?
I could call her on her cell phone, but she never turns it on. My best bet is to walk down the aisles looking left and right at every junction. Sometimes this approach requires half an hour, so my question is: how should I move?