Grid Walks and Direction Vectors
Move with dx, dy and stay in bounds.
Grid Walks and Direction Vectors is a free Coding Interview Prep lesson on CoddyKit — lesson 2 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Coding Interview Prep learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Walking on a Grid
Many simulations happen on a grid of rows and columns. A token starts somewhere and moves cell by cell following directions. 🗺️
Track Row and Column
Hold your position as a (r, c) pair. Row indexes the line top to bottom and column indexes left to right.
r, c = 0, 0Direction Vectors
Encode each move as a (dr, dc) vector. Adding it to your position shifts you one cell that way, no if-chains needed.
dr, dc = 0, 1 # move rightThe Four Neighbors
Store the four moves in arrays so you can loop over them. This is the standard up, down, left, right pattern.
DR = [-1, 1, 0, 0]
DC = [0, 0, -1, 1]Take One Step
To move, just add the chosen vector to your current cell. The same two lines work for any of the four directions.
r += DR[k]
c += DC[k]Stay In Bounds
Before stepping, check the cell is inside the grid. Rows run 0 to R-1 and columns 0 to C-1; anything else is off the board.
if 0 <= r < R and 0 <= c < C:
passDiagonals When Allowed
Some problems permit diagonal moves too. Add the four corner vectors to make an eight-direction neighbor set.
DR8 = [-1,-1,-1,0,0,1,1,1]
DC8 = [-1,0,1,-1,1,-1,0,1]Turning Left or Right
For a robot that turns, rotate its facing index instead of writing cases. Modulo keeps it cycling through the four directions.
facing = (facing + 1) % 4 # turn rightBlocked Cells and Walls
Check the grid value before moving. If a cell is a wall, skip it or stop, exactly as the rules describe.
if grid[r][c] == '#':
continueWrap-Around Grids
If the grid wraps, take coordinates modulo the size so the right edge connects back to the left edge smoothly.
r = (r + dr) % R
c = (c + dc) % CWhy Vectors Win
Direction vectors replace tangled if-else blocks with one tidy loop. Fewer branches means fewer bugs under contest pressure.
Quick Check
You walk a grid using direction vectors and must stay on the board.
Recap
Hold position as (r, c), move by adding direction vectors, loop the four neighbors, and always bounds-check before you step. 🚀
Frequently asked questions
Is the “Grid Walks and Direction Vectors” lesson free?
Yes — the full text of “Grid Walks and Direction Vectors” is free to read here on the web, and the Coding Interview Prep course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Coding Interview Prep course, upgrade to CoddyKit PRO.
What will I learn in “Grid Walks and Direction Vectors”?
Move with dx, dy and stay in bounds. You practise Coding Interview Prep with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Coding Interview Prep?
No prior experience is required. Coding Interview Prep on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Grid Walks and Direction Vectors” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Coding Interview Prep lesson?
Yes. Every Coding Interview Prep lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Model State and Step Forward
- Grid Walks and Direction Vectors
- Cycle Detection in Simulations
- Tame the Tricky Edge Cases