DSA · Theory

Array

Theory

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Array is a DSA topic. In plain words you use it for marks[0..n-1] in a class list. Don’t start with a slogan — start with that picture.

Smallest example: index access O(1). Type it, run it, and say what you see. If you can do that from memory, you know Array.

From the example next to this theory — Arrays give O(1) index access; matrices are arrays of arrays.

Trap — off-by-one on the last index. Fix that before you talk about advanced DSA.

Viva — what is Array? Then show index access O(1). Then name the trap.

Diagram

  index →  0    1    2
  array → [10,  20,  30]

Exam tip

What is Array? Show this: index access O(1). Trap: off-by-one on the last index.

arr = [10, 20, 30, 40]
print(arr[2], arr[-1])
matrix = [[1, 2], [3, 4]]
print(matrix[1][0])  # 3

Arrays give O(1) index access; matrices are arrays of arrays.