add pit

src/core/Pit.ts

@@ -0,0 +1,29 @@
+export class Pit {
+  stoneCount: number;
+
+  constructor(stoneCount = 0) {
+    this.stoneCount = stoneCount;
+  }
+
+  get isBank(): boolean {
+    return false;
+  }
+
+  public increaseStone(count = 1) {
+    this.stoneCount += count;
+  }
+
+  public decreaseStone(count = 1) {
+    this.stoneCount -= count;
+  }
+}
+
+export class Bank extends Pit {
+  constructor(stoneCount = 0) {
+    super(stoneCount);
+  }
+
+  override get isBank(): boolean {
+    return true;
+  }
+}