pythonType errorMedium

Counting map pins crashes on [x, y] points

Time: 0:00

BugFind the bug and fix the code

What it should do

count_unique_points(points) counts the different map pins. Each pin is [x, y]. Example: count_unique_points([[0, 0], [1, 2], [0, 0]]) → 2.

What happens instead

count_unique_points([[0, 0], [1, 2], [0, 0]]) crashes: TypeError: cannot use 'list' as a set element (unhashable type: 'list').

def count_unique_points(points):
    seen = set()
    for p in points:
        seen.add(p)
    return len(seen)

Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).

⏱️0:00

Hints

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Think & Test Cooldown

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Take a moment to read the bug symptom and trace the code with Run & Check before unlocking Hint 1.

Hint 2

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Hint 3

Unlocks after Hint 2

This bug belongs to the type errors pattern

Totals that concatenate, sorts that put 10 before 9, comparisons that refuse to run.

Learn the type errors pattern Step through your own code

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pythonType errorMedium

Counting map pins crashes on [x, y] points

Time: 0:00

BugFind the bug and fix the code

What it should do

count_unique_points(points) counts the different map pins. Each pin is [x, y]. Example: count_unique_points([[0, 0], [1, 2], [0, 0]]) → 2.

What happens instead

count_unique_points([[0, 0], [1, 2], [0, 0]]) crashes: TypeError: cannot use 'list' as a set element (unhashable type: 'list').

def count_unique_points(points):
    seen = set()
    for p in points:
        seen.add(p)
    return len(seen)

Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).

⏱️0:00

Hints

🏆 0 hints = Flawless Solve

Think & Test Cooldown

2:00 remaining

Take a moment to read the bug symptom and trace the code with Run & Check before unlocking Hint 1.

Hint 2

Unlocks after Hint 1

Hint 3

Unlocks after Hint 2

This bug belongs to the type errors pattern

Totals that concatenate, sorts that put 10 before 9, comparisons that refuse to run.

Learn the type errors pattern Step through your own code

Counting map pins crashes on [x, y] points

What it should do

What happens instead

More type errors to practise

Seen this error in your own code?

Counting map pins crashes on [x, y] points

What it should do

What happens instead

More type errors to practise

Seen this error in your own code?