Jump to content
BrainDen.com - Brain Teasers
  • 0

Reverse the order of 8 poisonous substances


Go to solution Solved by araver,

Question

8 very poisonous substances named s1 to s8 are kept in a safety room.
The substances are kept in ascending order (s1,s2,s3,s4,s5,s6,s7 and s8).
In the room there are 3 robots.

First robot can "rotate left" the order of the substances.
If the order is (a,b,c,d,e,f,g,h) the robot will make it (b,c,d,e,f,g,h,a)

Second robot can split the substances into 2 part then reverse the order of each part.
If the order is (a,b,c,d,e,f,g,h) the robot will make it (d,c,b,a,h,g,f,e)
But the robot is a bit broken, so the resulting order is a bit wrong.
The resulting order will become (d,c,a,b,h,g,f,e).

Third robot can split the substances into 4 part then reverse the order of each part
If the order is (a,b,c,d,e,f,g,h) the robot will make it (b,a,d,c,f,e,h,g)

Questions

If the 2nd robot is not broken, how many minimum step needed by using the robots to reverse the order into descending order? Show the steps!

After the 2nd robot is broken, how many minimum step needed by using the robots to reverse the order into descending order? Show the steps!

Edited by jasen
Link to post
Share on other sites

4 answers to this question

Recommended Posts

  • 1
  • Solution
Spoiler

For the first type/not-broken robot

5 steps  (a, b, c, d, e, f, g, h)
Robot 1: (b, c, d, e, f, g, h, a)
Robot 1: (c, d, e, f, g, h, a, b)
Robot 1: (d, e, f, g, h, a, b, c)
Robot 1: (e, f, g, h, a, b, c, d)
Robot 2: (h, g, f, e, d, c, b, a)

For the second type/broken robot, need to exploit that asymmetry 6 times, twice reordering in pairs and 6 left shifts, for a total of 14 steps.

14 steps (a, b, c, d, e, f, g, h)
Robot 2: (d, c, a, b, h, g, f, e)
Robot 1: (c, a, b, h, g, f, e, d)
Robot 3: (a, c, h, b, f, g, d, e)
Robot 1: (c, h, b, f, g, d, e, a)
Robot 2: (f, b, c, h, a, e, d, g)
Robot 2: (h, c, f, b, g, d, e, a)
Robot 1: (c, f, b, g, d, e, a, h)
Robot 1: (f, b, g, d, e, a, h, c)
Robot 2: (d, g, f, b, c, h, a, e)
Robot 2: (b, f, d, g, e, a, h, c)
Robot 1: (f, d, g, e, a, h, c, b)
Robot 3: (d, f, e, g, h, a, b, c)
Robot 1: (f, e, g, h, a, b, c, d)
Robot 2: (h, g, f, e, d, c, b, a)

 

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Answer this question...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...