Skip to main content
Engineering LibreTexts

5.5: Choosing a Structure

  • Page ID
  • \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)

    The doubly-linked implementation is better than ArrayList for adding and removing at the beginning, and just as good as ArrayList for adding and removing at the end. So the only advantage of ArrayList is for get and set, which require linear time in a linked list, even if it is doubly-linked.

    If you know that the run time of your application depends on the time it takes to get and set elements, an ArrayList might be the better choice. If the run time depends on adding and removing elements near the beginning or the end, LinkedList might be better.

    But remember that these recommendations are based on the order of growth for large problems. There are other factors to consider:

    • If these operations don’t take up a substantial fraction of the run time for your application — that is, if your applications spends most of its time doing other things — then your choice of a List implementation won’t matter very much.
    • If the lists you are working with are not very big, you might not get the performance you expect. For small problems, a quadratic algorithm might be faster than a linear algorithm, or linear might be faster than constant time. And for small problems, the difference probably doesn’t matter.
    • Also, don’t forget about space. So far we have focused on run time, but different implementations require different amounts of space. In an ArrayList, the elements are stored side-by-side in a single chunk of memory, so there is little wasted space, and computer hardware is often faster with contiguous chunks. In a linked list, each element requires a node with one or two links. The links take up space (sometimes more than the data!), and with nodes scattered around in memory, the hardware might be less efficient.

    In summary, analysis of algorithms provides some guidance for choosing data structures, but only if

    1. The run time of your application is important,
    2. The run time of your application depends on your choice of data structure, and
    3. The problem size is large enough that the order of growth actually predicts which data structure is better.

    You could have a long career as a software engineer without ever finding yourself in this situation.

    This page titled 5.5: Choosing a Structure is shared under a CC BY-NC-SA 3.0 license and was authored, remixed, and/or curated by Allen B. Downey (Green Tea Press) .

    • Was this article helpful?