Consider five holes in a line. One of them is occupied by a fox. Each night, the fox moves to a neighboring hole, either to the left or to the right. Each morning, you get to inspect a hole of your choice. What strategy would ensure that the fox is eventually caught?
start at the extreme left or right and work one hole at a time in the oposite direction. You may get lucky early on. but a maximum of 5 attempts would guarantee capture.
the sequence 2, 2, 3, 4, 4, 3, 2 will get the fox in 7 or fewer moves.
1) look in 2. In not there he's in 1, 3, 4 or 5
2) fox moves to 2, 3, 4 or 5. look in 2. If not there he's in 3, 4 or 5
3) fox moves to 2, 3, 4 or 5. look in 3. If not there he's in 2, 4 or 5
4) fox moves to 1, 3, 4 or 5. look in 4. If not there he's in 1, 3 or 5
5) fox moves to 2 or 4. look in 4. If not there he's in 2.
6) fox moves to 1 or 3. look in 3. If not there he's in 1.
7) fox must move to 2. look in 2. there he is!!!