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Q:Design a Hit-counter
“Design hit counter” problem has recently been asked by many companies including Dropbox and the question is harder than it seems to be. It includes a couple of topics like basic data structures design, various optimization, concurrency and distributed counter.
It should support the following two operations: hit and getHits.
HitCounter counter = new HitCounter();
// hit at timestamp 1.
counter.hit(1);
// hit at timestamp 2.
counter.hit(2);
// hit at timestamp 3.
counter.hit(3);
// get hits at timestamp 4, should return 3.
counter.getHits(4);
// hit at timestamp 300.
counter.hit(300);
// get hits at timestamp 300, should return 4.
counter.getHits(300);
// get hits at timestamp 301, should return 3.
counter.getHits(301);
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- eight way symmetry
- sqrt y for x + r
- no sqrt -> Bressanhams error:
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Can solution order number of living cells
parallelize it