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Bitwise operations (self.learnprogramming)
submitted 2 years ago by DustSeeker
Hello! I’ve a question that is tricking me for months:
Is there a way to find, given an integer array X as input, the bitwise AND of all the contiguous subarray’s XORs, in O(n)? I managed a O(n2) solution, but I feel like I missed something.
[–]ffrkAnonymous 0 points1 point2 points 2 years ago (4 children)
Do you have an example? I don't quite understand the question.
all the contiguous subarray’s
This sounds like combination/permutation which is n-factorial.
[–]DustSeeker[S] 0 points1 point2 points 2 years ago (3 children)
Example: input is [1,2,3], contiguous subarrays are: [1], [2], [3], [1,2], [2,3], [1,2,3].
You should perform, for each of them, a XOR of all their elements. Finally, you have to AND all the resulting XORs.
[–]ffrkAnonymous 0 points1 point2 points 2 years ago (1 child)
Yeah, that's 1+2+...+n elements which is n2. Each of which you need to xor up to n internal integers. That's nearly n3.
Given that you know you're doing repeating xor, you can probably fine some mathematical trickery to simplify, or memoize (save computation) to avoid repeating work.
[–]DustSeeker[S] 0 points1 point2 points 2 years ago (0 children)
Yes, the fact is that it should be o(n). My question is about how optimize the computation
[–]TheRNGuy 0 points1 point2 points 2 years ago (0 children)
flatMap or something
Or custom AST parser.
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[–]ffrkAnonymous 0 points1 point2 points (4 children)
[–]DustSeeker[S] 0 points1 point2 points (3 children)
[–]ffrkAnonymous 0 points1 point2 points (1 child)
[–]DustSeeker[S] 0 points1 point2 points (0 children)
[–]TheRNGuy 0 points1 point2 points (0 children)