Pearls ...

Frog Leap Brainteaser

Renee' referred the Frog Leap Brainteaser to me, to which she was referred by her sister.



I didn't time myself; but it took me something like 15 minutes and 4 or 5 tries to solve it the first time. Then it took me about 4 more tries to catalog all the moves.

Now, I know it's not that interesting and I'm sure Chinese school children solve it way faster than I did. But what is interesting (to me) is the heuristic I arrived at and that (I think) helped me solve it the first time. The idea is that for every move you make, you need to increase or preserve the number of face to face pairings of the frogs. If you have a frog facing the back of another frog, except for the final state, you'll get stuck with no moves.

Anyway, there are 2 solutions, depending on which color frog you move first. Here's one of them. First number the frog's rocks from 1 to 7, left to right. Then make the following jumps:

1. 3 - 4
2. 5 - 3
3. 6 - 5
4. 4 - 6
5. 2 - 4
6. 1 - 2
7. 3 - 1
8. 5 - 3
9. 7 - 5
10. 6 - 7
11. 4 - 6
12. 2 - 4
13. 3 - 2
14. 5 - 3
15. 4 - 5