DSA · Theory

Big O Notation in DS

Theory

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Big O Notation in DS

Don’t start Big O Notation in DS with jargon. Start with n vs n² on 10k rows. That is the whole point.

Do Big O Notation in DS once by hand. best / average / worst + extra memory. Change one input. Say the new result out loud.

Without Big O Notation in DS, a viva gets messy and n vs n² on 10k rows is hard to trust.

Big O Notation in DS shows up in a viva. Name n vs n² on 10k rows, not “a real-world scenario”.

Big O Notation in DS miss — saying ‘fast’ with no Big-O. Fix it before you talk about advanced DSA.

Place Big O Notation in DS next to nearby DSA work — best / average / worst + extra memory is the link.

Close Big O Notation in DS with — “If I skip it, n vs n² on 10k rows goes wrong like this: saying ‘fast’ with no Big-O.”

Exam tip

Say Big O Notation in DS in one breath, then best / average / worst + extra memory, then saying ‘fast’ with no Big-O.

Example

def demo(n):
    # O(1)
    x = n + 1
    # O(n)
    total = sum(range(n))
    # O(n^2)
    pairs = 0
    for i in range(n):
        for j in range(n):
            pairs += 1
    return x, total, pairs

print(demo(3))

Big O Notation in DS — big-O describes how work grows with input size — ignore constants.

Short notes

DefBig O Notation in DS — Dev uses it for n vs n² on 10k rows in a viva.
RuleBig O Notation in DS → best / average / worst + extra memory.
RememberBig O Notation in DS + time vs memory (a viva).
UseBig O Notation in DS in a viva (n vs n² on 10k rows).
TrapBig O Notation in DS — saying ‘fast’ with no Big-O.
ExBig O Notation in DS → n vs n² on 10k rows.

def demo(n): # O(1) x = n + 1 # O(n) total = sum(range(n)) # O(n^2) pairs = 0 for i in range(n): for j in range(n): pairs += 1 return x, total, pairs print(demo(3))

Big O Notation in DS

Example

Short notes

Questions

Big O Notation in DS

Example

Short notes

Questions