Simultaneous encodings for range and next/previous larger/smaller value queries

Abstract

Given an array of $n$ elements from a total order, we propose encodings that support various range queries (range minimum, range maximum and their variants), and previous and next smaller/larger value queries. When query time is not of concern, we obtain a $4.088n + o(n)$-bit encoding that supports all these queries. For the case when we need to support all these queries in constant time, we give an encoding that takes $4.585n + o(n)$ bits, where $n$ is the length of input array. This improves the $5.08n+o(n)$-bit encoding obtained by encoding the colored $2d$-Min and Max heaps proposed by Fischer~[TCS, 2011]. We first extend the original DFUDS [Algorithmica, 2005] encoding of the colored 2d-Min (Max) heap that supports the queries in constant time. Then, we combine the extended DFUDS of $2d$-Min heap and $2d$-Max heap using the Min-Max encoding of Gawrychowski and Nicholson [ICALP, 2015] with some modifications. We also obtain encodings that take lesser space and support a subset of these queries.