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Data Structures

Set

Add, check, or remove an item: O(1) on average. This is instant, no matter how many items you store.

The idea, in plain English

A set is like a guest list at a party door. Each name can appear only once. If you try to add the same name twice, nothing changes. It's already on the list.

How it works

  1. 1Add items. The set ignores duplicates automatically.
  2. 2Check if an item exists. You get a fast yes or no answer.
  3. 3Remove an item, or loop through everything that's left.

When you'd use it

Use a set to remove duplicates from a list, quickly check 'have I seen this before?', or track unique visitors to a page.

Common beginner mistakes

  • Don't expect a set to remember the order you added items. If order matters, sort the items before printing.
  • Don't assume printing a set always shows the same order. Python sets don't guarantee any order.

Try it — edit and run

Click the code to edit · press ⌘/Ctrl+↵ to run

Editable code. Tab and Shift+Tab indent. Press Escape, then Tab, to move focus out of the editor.

Expected output — hit Run to try it
Unique: amy bo cy
Count: 3
Has bo: yes
Has bo: no

See it in motion

Watch it dedupSetAdd, check, or remove an item: O(1) on average. This is instant, no matter how many items you store.
Incoming names
The set (unique only)
empty

Ready. Press play to build the set.

0/6
Processed
0
Unique
0
Duplicates
—
Test
Added / hitConsidering / matchRejected / missSettled

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