Add backend

backend/src/players/player-container.ts

@@ -0,0 +1,13 @@
+import { Player } from './player';
+
+export class PlayerContainer {
+  private socketIdToPlayer = new Map<string, Player>();
+
+  public addPlayer(player: Player) {
+    this.socketIdToPlayer.set(player.socketId, player);
+  }
+
+  public removePlayerBySocketId(socketId: string) {
+    this.socketIdToPlayer.delete(socketId);
+  }
+}