# Find neighbours in 2D grid

Posted on:June 6, 2022 at 04:06 AM

# Finding neighbours in 2D grid.

This is note to myself on how to get different ways to get neighbours from current cell in a grid.

Lets suppose that we have following grid represented by 2D array.

``````const grid = [
["Top Left", "Top Center", "Top Right"],
["Middle Left", "Middle Center", "Middle Right"],
["Bottom Left", "Bottom Center", "Bottom Righ"],
];``````

We want to get all 4 neighbours (top, right, bottom and left) from a given position (row and col), so if our position is row=1,col=1 then all 4 neighbours would be `[“Top Center”, “Middle Right”, “Bottom Center”, “Middle Left”]`. In case we are on the border of the grid then we will return only valid neighbours so for example in case of row=0, col=0 our neighbours would be `[“Top Center”, “Middle Left”]`. Lets write code for this:

``````const getNeighbours = (grid, x, y) => {
const results = [];
const directions = [
[-1, 0], // Left
[0, 1], // Down
[1, 0], // Right
[0, -1], // Up
];
for (const [dirX, dirY] of directions) {
const newX = x + dirX;
const newY = y + dirY;

if (newX > -1 && newX < grid.length && newY > -1 && newY < grid.length) {
// make sure grid has equal number of columns in rows
results.push([newX, newY]);
}
}
return results;
};
const grid = [
["Top Left", "Top Center", "Top Right"],
["Middle Left", "Middle Center", "Middle Right"],
["Bottom Left", "Bottom Center", "Bottom Righ"],
];
getNeighbours(grid, 1, 1).forEach(([row, col]) => console.log(grid[row][col]));
/*
Top Center
Middle Right
Bottom Center
Middle Left
*/``````

To get neighbours in all eight directions we can use the following directions array:

``````const directions = [  [-1, 0], // West
[-1, 1], // Northwest
[0, 1], // North
[1, 1], // Northeast
[1, 0], // East
[1, -1], // Southeast
[0, -1], // South
[-1, -1], // Southwest
];``````

Lets take a look at another similar implementation in which we will use the following direction array: `[0, 1, 0, -1, 0]` the rest of the code remains the same here is what will change

``````const directions = [0, 1, 0, -1, 0];
for (let i = 0; i < directions.length - 1; i++) {
const newX = x + directions[i];
const newY = y + directions[i + 1];

if (newX > -1 && newX < grid.length && newY > -1 && newY < grid.length) {
// make sure grid has equal number of columns in rows
results.push([newX, newY]);
}
}``````

For eight directions you can use the following array: `[0, 1, -1, 1, 1, 0, -1, -1, 0]`

So these are the two most common ways to find neighbours in of a cell in grid.