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Microsoft Software Development Engineer I Interview Question

I interviewed in Seattle, WA and was asked:
"there is an array with 99 length long, each spot will have number from 1-100, number will never repeat on the array. Give as many way as possible to find the missing number."
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Answers & Comments

of 4

Add up all number in the array and find the difference between the sum of 1 to 100.

- Interview Candidate on Jun 4, 2012
of 2

Another way since the interviewer asked for as my solutions as possible

1. Create another array of 100 elements and initialize to 0
2. Traverse through the first array and mark the corresponding spot in the second array
3. Now traverse through the second array and find the spot that is still marked as 0 - that is your missing element

Note: You'll have to do a subtract by 1 since the numbers are from 1-100 and your array count will be from 0 to 99.

- Anon on Jun 12, 2012
of 1

sum of 1 to 100 can be got by using Gauss's formula n(n+1)/2. If we subtract the sum of all numbers in the array with the result we got from formula, it's the answer.

- Bharath on Jun 19, 2012

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