IPVGO: Prevent tiny islands surrounded by offline nodes during initial board generation (#2310)

src/Go/boardState/offlineNodes.ts

@@ -3,6 +3,9 @@ import type { Board, BoardState, PointState } from "../Types";
 import { Player } from "@player";
 import { boardSizes } from "../Constants";
 import { WHRNG } from "../../Casino/RNG";
+import { getAllChains } from "../boardAnalysis/boardAnalysis";
+import { updateChains } from "./boardState";
+import { GoColor } from "@enums";
 
 type rand = (n1: number, n2: number) => number;
 
@@ -36,6 +39,8 @@ export function addObstacles(boardState: BoardState) {
   boardState.board = ensureOfflineNodes(boardState.board);
 
   boardState.board = resetCoordinates(boardState.board);
+
+  boardState.board = removeIslands(boardState.board);
 }
 
 export function resetCoordinates(board: Board) {
@@ -52,6 +57,24 @@ export function resetCoordinates(board: Board) {
   return board;
 }
 
+/**
+ * Removes all tiny islands of empty points (2 or fewer) from the board
+ * @param board
+ */
+export function removeIslands(board: Board) {
+  updateChains(board, true);
+  const chains = getAllChains(board);
+
+  for (const chain of chains) {
+    if (chain.length <= 2 && chain[0]?.color === GoColor.empty) {
+      for (const point of chain) {
+        board[point.x][point.y] = null;
+      }
+    }
+  }
+  return board;
+}
+
 function getScale(board: Board) {
   return boardSizes.indexOf(board[0].length);
 }

test/jest/Go/boardState.test.ts

@@ -1,7 +1,7 @@
 import { getNewBoardState, makeMove, passTurn, updateCaptures } from "../../../src/Go/boardState/boardState";
 import { GoColor, GoOpponent } from "@enums";
 import { boardFromSimpleBoard, simpleBoardFromBoard } from "../../../src/Go/boardAnalysis/boardAnalysis";
-import { resetCoordinates, rotate90Degrees } from "../../../src/Go/boardState/offlineNodes";
+import { removeIslands, resetCoordinates, rotate90Degrees } from "../../../src/Go/boardState/offlineNodes";
 import { bitverseBoardShape } from "../../../src/Go/Constants";
 import { getEmptyHighlightedPoints } from "../../../src/Go/Go";
 
@@ -52,6 +52,12 @@ describe("Board analysis utility tests", () => {
     expect(boardWithNoRouters).toEqual(specialBoardTemplate);
   });
 
+  it("removes tiny empty point chains from initial board", () => {
+    const board = boardFromSimpleBoard([".#...", "##...", ".....", "...##", "..#.."]);
+    const cleanedBoard = removeIslands(board);
+    expect(simpleBoardFromBoard(cleanedBoard)).toEqual(["##...", "##...", ".....", "...##", "..###"]);
+  });
+
   it("Correctly applies moves made", () => {
     const result = getNewBoardState(5, GoOpponent.Daedalus, false);
     makeMove(result, 1, 1, GoColor.black);