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Hard Arrays Cheat Sheet

  • Quick summary: a collection that stores elements in order and looks them up by index.
  • Also known as: fixed array, static array.
  • Important facts:
    • Stores elements sequentially, one after another.
    • Each array element has an index. Zero-based indexing is used most often: the first index is 0, the second is 1, and so on.
    • Is created with a fixed size. Increasing or decreasing the size of an array is impossible.
    • Can be one-dimensional (linear) or multi-dimensional.
    • Allocates contiguous memory space for all its elements.
  • Pros:
    • Ensures constant time access by index.
    • Constant time append (insertion at the end of an array).
  • Cons:
    • Fixed size that can't be changed.
    • Search, insertion and deletion are O(n). After insertion or deletion, all subsequent elements are moved one index further.
    • Can be memory intensive when capacity is underused.
  • Notable uses:
    • The String data type that represents text is implemented in programming languages as an array that consists of a sequence of characters plus a terminating character.
  • Time complexity (worst case):
    • Access: O(1)
    • Search: O(n)
    • Insertion: O(n) (append: O(1))
    • Deletion: O(n)
  • See also:

Show Cheatsheet

Hard Arrays Definition: A basic linear data structure that holds a fixed number of containers to store data.

Interview Problems

Why do I see duplicate challenges? You'll see duplicates because a question may fall into different categories. We keep them here because we believe that it is good to sporadically review old problems. They are optional if already completed-- but reviewing them (and more importantly re-doing them with the new knowledge) will ensure that you've internalized the patterns.

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