Finding Frequent Elements in Compressed 2D Arrays and Strings

  title={Finding Frequent Elements in Compressed 2D Arrays and Strings},
  author={Travis Gagie and Meng He and J. Ian Munro and Patrick K. Nicholson},
We show how to store a compressed two-dimensional array such that, if we are asked for the elements with high relative frequency in a range, we can quickly return a short list of candidates that includes them. More specifically, given an m × n array A and a fraction α > 0, we can store A in O ( mn(H + 1) log(1/α) ) bits, where H is the entropy of the elements’ distribution in A, such that later, given a rectangular range in A and a fraction β ≥ α, in O(1/β) time we can return a list of O(1… CONTINUE READING