What is a Sparse Array? When is it useful?

Difficulty: 5/10

memory efficiency, index mapping, use cases

Sparse Arrays

A sparse array is a logical array where most positions contain no meaningful value. Instead of allocating memory for every position, a sparse representation stores only the non-default entries, often using a map, dictionary, or coordinate-value structure.

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Useful when the index space is large but populated positions are few.
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Common in sparse matrices, graphs, scientific computing, and recommendation systems.
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Can substantially reduce memory consumption.
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Lookup complexity depends on the chosen sparse representation.
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A normal dense array may be preferable when most positions contain values.

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0-2 years experience

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