Add coordinate utils

utils/coordinates.ts

@@ -24,3 +24,57 @@ export function isCoordinateEqual(
 ): boolean {
   return b[0] === a[0] && b[1] === a[1];
 }
+
+export type DirectNeighbours = 'top' | 'left' | 'right' | 'down';
+
+export type DiagonalNeighbours =
+  | 'topLeft'
+  | 'topRight'
+  | 'downLeft'
+  | 'downRight';
+
+/**
+ * Get all eight adjacent cells from a starting cell.
+ * Returns undefined, when the cell is invalid (out of bounds).
+ * @param rows Input xy-Matrix, string array
+ * @param startX Center cell x Coordinate
+ * @param startY Center cell y Coordinate
+ */
+export function getAdjacent(
+  rows: string[],
+  startX: number,
+  startY: number
+): Record<DirectNeighbours | DiagonalNeighbours, string | undefined> {
+  const top = rows[startY - 1]?.[startX];
+  const right = rows[startY]?.[startX + 1];
+  const down = rows[startY + 1]?.[startX];
+  const left = rows[startY]?.[startX - 1];
+
+  const topLeft = rows[startY - 1]?.[startX - 1];
+  const topRight = rows[startY - 1]?.[startX + 1];
+  const downLeft = rows[startY + 1]?.[startX - 1];
+  const downRight = rows[startY + 1]?.[startX + 1];
+
+  return { top, right, left, down, topLeft, topRight, downLeft, downRight };
+}
+
+/**
+ * Find all xy-Coordinates of a digit or custom regex match.
+ * @param rows Input xy-Matrix, string array
+ * @param digit Digit to search for, or custom regex pattern
+ */
+export function findCoordsOfDigit(
+  rows: string[],
+  digit: string | RegExp
+): Coordinates {
+  return rows.reduce<Coordinates>(
+    (coords, row, y) =>
+      row
+        .matchAll(typeof digit === 'string' ? new RegExp(digit, 'g') : digit)
+        .reduce(
+          (coordinates, m) => [...coordinates, [m.index, y] as Coordinate],
+          coords
+        ),
+    []
+  );
+}