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Puzzle: 100-story building, identify the lowest floor for which a marble will break?

+7 votes

You have a 100-story building and a couple of marbles. You must identify the lowest floor for which a marble will break if you drop it from this floor.

  1. How fast can you find this floor if you are given an infinite supply of marbles?
  2. What if you have only two marbles?
posted Jan 28, 2014 by Merry

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1 Answer

+1 vote

Use Binary Search:

first step- 100/2=50, try to drop from 50th floor. not 1 cases

1- it breaks 2- It did not

If it breaks then obviously the floor should be below 50 otherwise above 50

Then again repeat Binary Search...

so in this way number of operaions = log (base 2) n, where n=100

answer Jan 28, 2014 by Atul Mishra

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