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NewSimulations

Watch your code run, one step at a time.

57 simulations of the problems you already practise, from Binary Search to N-Queens. They run on your own values, light up the line that is running, and give a plain reason for every step.

Try it in a chatFind your problem

Try one right here

This is the real simulation, not a video. Press play, or step with ← and →.

Try it on your own values

Built so the idea clicks

Show bubble sort on 7, 2, 9, 4
7
2
9
4

Your numbers, not a textbook's

Ask with the values from your problem. The simulation runs on exactly those.

7
2
9
4
compare 7, 27 > 2, so we swap them.

A reason for every step

What happened on the left, and why on the right, in one plain sentence.

1for i in range(n):
2 for j in range(n - 1 - i):
3 if a[j] > a[j + 1]:
4 a[j], a[j + 1] = a[j + 1], a[j]

The code moves with the picture

The line that runs lights up as you step, so you see what the code does, not just what it says.

Variables
i0
j1
a[2, 7, 9, 4]
swappedTrue

Every variable, in view

Open Variables and watch i, j, the stack or the queue change, with the Big-O count at the end.

[ ][1][ ][1, 2][1][2][ ]

Recursion you can see

Backtracking is drawn as a tree: every choice is a branch, and every step back is visible.

←back
Spaceplay
→next
0.5×1×2×

At your pace

Play, pause, step back or change speed. On a laptop, ← → and Space do it too.

Practising on LeetCode or GeeksforGeeks?

Find your problem. Each simulation covers the core idea of the problems listed with it.

  • Binary search

    Arrays and sorting

    lo, mid and hi halve a sorted window every step.

    • LC704. Binary Search
    • LC35. Search Insert Position
    • LC278. First Bad Version
    Try it

  • Kadane's algorithm

    Arrays and sorting

    At each cell the run either grows or starts fresh, keeping the best total.

    • LC53. Maximum Subarray
    • LC918. Maximum Sum Circular Subarray
    • GfGKadane's Algorithm
    Try it

  • Reverse a list in place

    Linked lists

    prev, curr and next flip one arrow per step.

    • LC206. Reverse Linked List
    • LC92. Reverse Linked List II
    • LC234. Palindrome Linked List
    Try it

  • Level-order traversal

    Trees

    A queue visits the tree one level at a time.

    • LC102. Binary Tree Level Order Traversal
    • LC199. Binary Tree Right Side View
    Try it

  • Topological order with Kahn's algorithm

    Graphs

    In-degrees drain; nodes with none left come out next.

    • LC207. Course Schedule
    • LC210. Course Schedule II
    • GfGKahn's algorithm for Topological Sorting
    Try it

  • Subsets

    Backtracking

    Choose, explore, un-choose; every call is a subset.

    • LC78. Subsets
    Try it

Release notes

What shipped, and when.

  1. 20 October 2026Latest

    Backtracking, drawn as a recursion tree

    Eight classic backtracking problems, from Subsets to N-Queens. Every choice is a branch, every step back is visible, and the code moves with the tree.

    • Subsets
    • Subsets II
    • Permutations
    • Combination Sum
    • Combination Sum II
    • Letter Combinations of a Phone Number
    • Palindrome Partitioning
    • N-Queens
  2. 16 October 2026

    49 step-by-step simulations

    Arrays, sorting, stacks, queues, heaps, linked lists, trees and graphs. Ask for one in any chat and it runs on your own values, with a reason for every step.

    • Traverse an array
    • Linear search
    • Binary search
    • Swap two cells
    • Insert at an index
    • Delete at an index
    • Selection sort
    • Bubble sort
    • Insertion sort
    • Quicksort
    • Merge sort
    • Three-way partition
    • Two pointers
    • Prefix sums
    • Kadane's algorithm
    • Stack push and pop
    • Next greater element
    • Queue on an array
    • Circular queue
    • Queue from two stacks
    • Sliding window maximum
    • Insert into a max-heap
    • Build a heap
    • Extract the maximum
    • Keep the k largest
    • Build a linked list
    • Insert at a position
    • Delete a node
    • Traverse a list
    • Search a list
    • Reverse a list in place
    • Reverse a list with recursion
    • Detect a cycle
    • Remove the head
    • Delete the tail of a doubly linked list
    • Build a binary search tree
    • Search a binary search tree
    • Delete from a binary search tree
    • Insert into an AVL tree
    • In-order traversal
    • Pre-order traversal
    • Post-order traversal
    • Level-order traversal
    • Breadth-first search
    • Depth-first search
    • Dijkstra's shortest paths
    • Dijkstra on two-way roads
    • Topological order with Kahn's algorithm
    • Topological order with DFS

Ask for any of them, any time

In any chat, name the algorithm and your values, like “show me merge sort on 38, 27, 43, 3”. Your tutor draws it for you.

Start a chat