Count Sketch
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Python Week 1: the first filter for runtime behavior
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# Count Sketch ## Algorithm Maintain a $t \times k$ array $C$ of counters and $t$ hash functions $h_j$ mapping items to $[k]$, plus $t$ sign hash functions $g_j$ mapping items to $\{-1, +1\}$. **Update:** For item $i$, $C[j][h_j(i)] += g_j(i)$ for $j = 1, \dots, t$.
Count Sketch
Algorithm
Maintain a array of counters and hash functions mapping items to , plus sign hash functions mapping items to .
Update: For item , for .
Query:
Heavy Hitters
Find items with frequency (where is stream length).
Misra-Gries: space, guarantees .
Count-Min + Heap: Track top items in a min-heap alongside sketch.
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