The Direct-Access Array

The Direct-Access Array is one of the simplest data structures. It stores data at the index corresponding to the value of the data itself. Typically, the stored type is a boolean flag indicating the existence of this value. Utilizing a Direct-Access Array yields optimized constant time complexity when storing and reading data (by incrementing the index and accessing the memory that the index points to). It also can be used to detect duplicates. When we try storing a number and the boolean flag is true, we find a duplicate. This characteristic can be used to replace the HashSets in the cases that the largest number is known to be bounded within a reasonable range. Aside from the replacement optimization, the special array is used in the "buckets" structure in the highly efficient Radix Sort algorithm.
Insight: Simple data structures often deliver high performance but often cannot implement sophisticated operations. We should consider these simple data structures when facing limited computational resources and pursuing highly efficient algorithms.