Dry Run Whiteboard for LeetCode

What it does

Drawn from the problem

One click on an example, or on the Testcase panel with your own edits, and its inputs appear as the right structures, named after their parameters, with the expected output beside them.

Every structure

Linked lists with cycles, binary trees from level order, n-ary trees, edge and adjacency lists, weighted and directed graphs, and design problems as a table of calls. Change what something became with one click.

Pointers and steps

Add pointers like i, j, lo, mid, slow and fast, and walk them with the arrow keys. Press . for the next step and , to go back: every step remembers its values, pointers and marks.

The trace fills itself

One row per step and one column per pointer and variable, like "2 (11)". Type over any cell, mark cells as visited, done or the answer, and play the steps back.

A real whiteboard too

A pen with pressure, a highlighter, shapes, arrows that stick to cells, text, sticky notes and a laser pointer. Drag the Array tool across for as many boxes as you need.

Type it, it's drawn

Press / and type /tree [3,9,20,null,null,15,7], /dp "abcde" "ace" or /graph 0-1 1-2. Paste [2,7,11,15] and it becomes an array.

Beside your code

Dock the board over the description or over the code, float it or go full screen. Glass mode lets you draw over the whole page, and you can highlight the statement in three colours.

Every board kept

Each problem keeps its own board, contest problems too, saved automatically. Export a PNG for your notes, and back up or restore all your boards from the popup.