ZERO / HERO
A light switch

O(1) — Constant

The analogy

Flipping a light switch takes the same moment whether the house has one bulb or a thousand. The size of the problem simply does not enter into it.

Visualizer

The light switch

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SWITCH
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4 bulbs, one switch. Flipping it is one operation.n = 4, operations = 1

def toggle(lights):
    lights.on = not lights.on     # one operation

# n = 4 bulbs      -> 1 operation
# n = 1_000_000    -> 1 operation

d = {"k": 1}
d["k"]        # O(1)
a[i]          # O(1)
stack.append(x)  # amortised O(1)
Check yourself

Which is O(1)?