In The Times article on bicycle theft, a computer scientist outlines how he tried to convince police to use mathematics to search for stolen bicycles.
Bike theft is one of those crimes that the police don’t pay much attention to. In Cambridge, England, where the computer scientist lives, police won’t investigate CCTV footage of her if they can’t pinpoint the exact time frame of the theft.
A police spokesperson said after one theft in 2017, “Current police policy is not to comb through CCTV if the time exceeds four hours.
“The time frame in which the theft occurred is 10 hours, and we don’t have the resources to hunt through 10 hours of footage.”
However, as computer scientists point out, you don’t have to look hard, you have to look smart. Suppose you have a rough idea that your bike has been stolen in the last two days. You don’t have to sit there and fast-forward the footage until you spot someone dressed like a stock photo bike thief approaching your bike.
With Binary Search (or Binary Chop, if you want a cooler name), you can go through the footage and find the bike thief in a fraction of the time.
I want to find an item in a sorted list of items. To find it using binary search, go to the midpoint and see where it is in the list of items. Then go to the halfway point in the half of the list that you know contains the item and repeat until you find it.
For the cyclist, his attempt to persuade the police was to go to the halfway point of a long CCTV footage to see if the bike was there. If so, you’ll have to skip to his three-quarters of the footage, check again, and repeat the process until you find the bike quickly.
According to The Times, he noted that “if CCTV footage were to be traced back to the dawn of mankind, it probably would have taken only an hour to find the moment of the theft.”
Apparently, this didn’t go over well with the police.
[H/T: The Times]