Lens
Watch code run one line at a time: every variable, array, table, linked list and tree drawn as it changes. It's built into every room, too: write any code and press Visualize.
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Linked lists·O(n)
Reverse a linked list
Walk the list once, turning every next pointer around.
Change anything you like, then press Visualize⌘↵
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Lens records up to 1,000 steps. The first Python run downloads Python, which takes a few seconds.
Concept library
40 classic algorithms and data structures, each ready to watch in Python, JavaScript or TypeScript.