Add problem pool to tree provider

src/explorer/LeetCodeTreeDataProvider.ts

@@ -14,6 +14,8 @@ import { LeetCodeNode } from "./LeetCodeNode";
 
 export class LeetCodeTreeDataProvider implements vscode.TreeDataProvider<LeetCodeNode> {
 
+    private problemPool: Map<string, IProblem>; // maintains the ownership of all problems.
+
     private treeData: {
         Difficulty: Map<string, IProblem[]>,
         Tag: Map<string, IProblem[]>,
@@ -32,6 +34,10 @@ export class LeetCodeTreeDataProvider implements vscode.TreeDataProvider<LeetCod
         this.onDidChangeTreeDataEvent.fire();
     }
 
+    public getProblem(id: string): IProblem | undefined {
+        return this.problemPool.get(id);
+    }
+
     public getTreeItem(element: LeetCodeNode): vscode.TreeItem | Thenable<vscode.TreeItem> {
         if (element.id === "notSignIn") {
             return {
@@ -102,13 +108,16 @@ export class LeetCodeTreeDataProvider implements vscode.TreeDataProvider<LeetCod
 
     private async getProblemData(): Promise<void> {
         // clear cache
+        this.problemPool = new Map<string, IProblem>();
         this.treeData = {
             Difficulty: new Map<string, IProblem[]>(),
             Tag: new Map<string, IProblem[]>(),
             Company: new Map<string, IProblem[]>(),
             Favorite: [],
         };
         for (const problem of await list.listProblems()) {
+            // Add every problem to problem pool
+            this.problemPool.set(problem.id, problem);
             // Add favorite problem, no matter whether it is solved.
             if (problem.isFavorite) {
                 this.treeData[Category.Favorite].push(problem);