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Comment by ape4 | Hacker News Reader

In Java this prints -4

    int [] nums = { 2, -2, 0, 0 };
    int dup = findDupe(nums);
    System.out.println("dup="+dup);

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This only works if the numbers are in a known range (say sequential from 1 to 100), and you XOR in the index (plus 1) as well. Then each number is XOR'd two times, except the duplicate, which is XOR'd 3 times (and thus remains at the end). The fact that the code is wrong shows why this question is a very bad interview question.

EDIT

The given code works to find the only non-duplicate item in a list (perhaps that was what was intended)

yes,that was the intention, I can't edit by now. I had to leave fast and then got "noprocast" on and couldn't reply / correct

but it is nice that people got what I said through the lines!

it should have been called findNonDupe and the var should have been called nonDup.

Hope I'll do better in a real interview ;)

The problem was formulated as to find the only non-duplicate number.

Yes, my wife was waiting on me for lunch so I made tons of typos, yes I meant find the only non duplicate number. and I meant O(1) memory O(N) time complexity.

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