Wednesday, November 17, 2010

Arrays comparison. don't always sort them.

Two arrays are given A[n] and B[n+1]. Array A contains n integers and B contains n+1 integers of which n are same as in array B but in different order and one extra element x. Find x.

5 comments:

  1. XOR elements of A with those in B. Whatever remains is the extra element? Are the n elements distinct?

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  2. Very easy of course. But it makes me think of interesting followup variants.

    What if there were TWO extra integers in B. Can you find them BOTH easily?

    What if A and B are the same length but one element differed? Can you find that element in both A and B easily?

    The obvious programmer solution is a hash table, but that doesn't have the elegance of a much more clever method!
    Hint below:



    (Hint: no hash, no sorting, O(1) storage, use a little algebra.)

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  3. Once again xor bit operation comes in handy.
    a[0] xor a[1] xor .... a[n] xor b[0] xor b[1] xor ... b[n+1] will give the correct answer

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