Cups

Computer Science Level 2

You have 12 cups on a table, all placed facing up. Your objective is to flip over all of the cups.

In each move, you have to flip over exactly 5 cups. For example, you can take 5 cups. If these cups are facing up you can flip then to these cups becomes facing down. If these cups are facing down you can flip then to these cups becomes facing up.

What is the minimum number of moves you need to make in order to make all the cups face down?


The answer is 4.

Victor Paes Plinio by Victor Paes Plinio , 21, Brazil

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3 solutions

Harman Arora
Jul 22, 2014

First flip 5 cups down.. Then flip 4 of those 5 cups up and 1 of others down.. Now we have 2 cups down in 2 moves.. Rest 10 cups facing up will need next two more moves to flip them all down.. Total 4 moves..!!

1 Helpful 0 Interesting 0 Brilliant 0 Confused

problem *Flip first 5 cups (1,2,3,4,5) *Now Flip Cup no. 3,4,5,6,7 *Again Flip Cup no. 4,5,6,8,9 -Now you have Cup no. 3,6,10,11,12 facing upwards, while rest face Downwards- *Hope you Know the next step, turn the remaining 5 cups.

Vishnu Kaushal - 6 years, 10 months ago
Manit Kapoor
Oct 2, 2014

Consider 1 as cup open upwards and 0 as cup flip downwards now 12 cups are shown as 1 1 1 1 1 1 1 1 1 1 1 1 first 5 cups flipped 0 0 0 0 0 1 1 1 1 1 1 1 -1
cups from 3rd to 7th are flipped 0 0 1 1 1 0 0 1 1 1 1 1 -2
cups from 7th to 11th flipped 0 0 1 1 1 0 1 0 0 0 0 1 -3
left 5 cups are flipped 0 0 0 0 0 0 0 0 0 0 0 0 -4


0 Helpful 0 Interesting 0 Brilliant 0 Confused
Alex Romero
Jul 27, 2014

Any idea of how to write this in an algorithm?

0 Helpful 0 Interesting 0 Brilliant 0 Confused

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