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Twitter Software Engineer Intern Interview Question

I interviewed in Palo Alto, CA and was asked:
"given an array of numbers and a number k, find if two numbers in the array add up to k. Running time, space complexity, standard questions."
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Part of a Software Engineer Intern Interview Review - one of 203 Twitter Interview Reviews

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Naive solution:
for i in range(len(array)):
   for j in range[i+1, len(array)]:
       if array[i] + a[j] == k: return true

but this is O(N^2)

we can do better if we hash the elements of the array so we can check in constant time if they are present.
map = { }
for i in array:
   map[i] = true;

for i in array:
   if map[k - i] then return true

this algorithm is O(N)
- anon on Dec 16, 2013 Flag Response

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