快猫短视频

#217 Vicious circle

Set by Brian Hobbs

It made sense at the time. The enemy was coming and Neville the Mighty But Not That Bright had created a circular moat in which he placed a fast-swimming, flesh-eating moat monster. He stood at the centre of the island, sword in hand, guarding the only bridge, and ready to fight whoever dared to cross. The plan was foolproof鈥� until the enemy burned down the bridge.

Now, Neville is stranded on an island encircled by a moat with a monster in it. He can just barely run and jump the moat, but the monster swims four times as fast as Neville can run and can sense where he is at all times. If Neville tries to jump the moat while the monster is directly beneath him, he will be snatched out of the air like a sausage being caught by a dog. Is Neville doomed by his own plan or is there a chance of escape?

Solution next week

#216 Game of stones

Solution

To win, you must ensure that, after each of your moves, the difference between the positions of adjacent stones is always an odd number. For example, you could move the stone on 40 to 9, so the stones are on 0, 9 and 20, with gaps of nine and 11 positions between them. When your adversary plays, they will forever be forced to leave one odd difference and one even difference. For instance, if your opponent moves the stone at 0 to 14, the positions are now 9, 14 and 20, and the differences are five and six. You can always leave two odd differences between the 鈥渆ven鈥� pair.

The game ends when the neighbouring stones are all just one position apart. Since only you can achieve this odd-odd pattern, you will have the final, winning move.