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## Interview Question

Interview(Student Candidate)

# You have 99 distinct numbers from 1-100, how would you find

which number is missing?

0

Depends on whether the numbers are sorted or not.

Interview Candidate on Oct 28, 2010
0

I would average them out and multiply their difference from 50.5 by 100 to find the missing number

honeyoak on Feb 19, 2011
2

I would calculate total and substract it from total of full list. Example: Calculate total for original list 1,2,3,4,..100 = 5050 Let's assume the missing mnumber is 20 Calculate total of given list = 5030 The missing number is 5050 - 5030 = 20

kebzor on May 1, 2011
0

kebzor is correct. same principle applies to any list of consecutive n integers (starting from 1). e.g. if list is 1-10, then sum is 55 so the missing number x = 55 - (sum of given nine numbers). side question: what if you are missing two numbers from 1-10; what can you say?

anon on May 16, 2013
0

in fact, as long as the list is of finitely many consecutive distinct integers, the above method works. using factorization, there is also a unique solution to solving for two missing numbers. i don't know of an elegant solution for k missing numbers in general.

anon on May 16, 2013