The problem of determining whether this is a piece of land in land map array - node.js

Question

This is an issue in typescript.
As such, I have a variable with various string entries in the form of x, y position.
["3,3","3,4","3,5","2,3","2,4","2,5","-1,-2","-2,- 2","-2,-1"]
I want to know if this piece of land is one piece or several pieces.

Answer 1

Establish the mathematical guidelines
Two tiles are neighbors if they are different by a value of 1 in either x or y (but not both).
If you only need to determine whether they are all connected, then you really need to determine that every pair of vertices have a path from one to the other.
Plan the coding implementation
One way to go about this is to create an empty land mass array, start by adding a single tile from the source array, then you add each tile in the source array to the land mass array if it is a neighbor to one of the items in the land mass. If it does not have a neighbor, it may just not have one on the land mass yet, so we add it to a deferred queue and return to those when we have exhausted the source.
This method has O(n^2) complexity, but maybe someone else has a better solution computationally.
Give it a try
let source = [...coordinateArray]; // from prop or API or wherever
let landMass = [];
let deferred = [];
while(source.length) {
// add the tile if it has a neighbor on the land mass
// defer the tile if it does not have a neighbor on the land mass
source.forEach(pair1 => {
const [x1, y1] = pair1.split(",");
const hasNeighbor = !landMass.length || landMass.some(pair2 => {
const [x2, y2] = pair2.split(",");
// return "true" if off by 1 in x or y position and 0 in the other
return (Math.abs(x1 - x2) === 1 && y1 === y2) || (Math.abs(y1 - y2) === 1 && x1 === x2);
});
// push tile to landMass or to defer queue
if(hasNeighbor) {
landMass.push(pair1);
} else {
deferred.push(pair1);
}
});
// if source is now the same as deferred,
// then nothing was added to the land mass
// therefore it is disconnected and we can break out
if(source.length === deferred.length) {
break;
}
// otherwise, we have exhausted the source,
// so we move the "deferred" to the "source"
// and empty the "deferred" to repeat
source = [...deferred];
deferred = [];
// if the deferred queue had length 0,
// then we will break out of the while loop
}
// if the source has length > 0, then some tiles could not be mapped
// in that case, it is disconnected
// if the source has no length, then everything was mapped to the land mass
// in that case, it is connected
const allTilesAreConnected = !source.length;