Power Tools: Sets & Counting Dicts 🧰

Remember counting unique words with a seen-list and a nested loop? You earned that sweat — and now you earn the reward. This unit hands you two power tools that turn yesterday's hardest problems into three-liners.

The set: a bag that refuses repeats

album = set()
album.add("star")
album.add("star")   # bounces off!
len(album)          # 1

Make one from any list with set(items). Ask membership with in — instantly, no loop. And sets know friendship tricks:

a & b   # in both
a | b   # in either
a - b   # in a but not b
a <= b  # is a completely inside b?

The dict as a tally counter

You know dicts. Here's their superpower — THE counting line:

counts = {}
for item in items:
    counts[item] = counts.get(item, 0) + 1

.get(key, 0) reads a count that might not exist yet. With a tally dict plus your trusty best-so-far loop, you can crown winners, spot loners, and balance candy economies.

Several problems here are TURBO versions of puzzles you've already solved the slow way. Same puzzle, new tool — feel how much lighter it gets. That feeling is why tools exist. ⚡