https://leetcode.com/problems/matrix-cells-in-distance-order

function allCellsDistOrder(rows: number, cols: number, rCenter: number, cCenter: number): number[][] {
    const getKey = ([x, y]: [number, number]) => `${x}_${y}`;
    const inRange = ([x, y]: [number, number]) => x < rows && y < cols && x >= 0 && y >= 0;
    const getNeighbors = ([x, y]: [number, number]): [number, number][] => ([ [x+1, y], [x-1, y], [x, y+1], [x, y-1] ]);

    // add at the end, iterate from the front, which means we'll end up in order
    const all: [number, number][] = [ [rCenter, cCenter ] ];
    const seen = new Set<string>([getKey(all[0])]);
    for(let i=0; i<all.length; i++) {
        for(const n of getNeighbors(all[i])) {
            if (!inRange(n)) continue;
            const key = getKey(n);
            if (seen.has(key)) continue;
            seen.add(key);
            all.push(n);
        }
    }

    return all;
};