Grade school

typescript/grade-school/grade-school.ts

@@ -0,0 +1,35 @@
+export class GradeSchool {
+  private _roster: Record<number, string[]> = {};
+
+  roster(): Record<number, string[]> {
+    return JSON.parse(JSON.stringify(this._roster));
+  }
+
+  get grades(): number[] {
+    return Object.keys(this._roster) as unknown as number[];
+  }
+
+  add(name: string, grade: number): void {
+    const addUniqueValue = <T extends any>(
+      array: T[] | undefined,
+      value: T
+    ): T[] => [...new Set<T>([...(array || []), value])];
+
+    const allGrades = addUniqueValue(this.grades, grade);
+
+    this._roster = allGrades.reduce(
+      (newRoster, rosterGrade) => ({
+        ...newRoster,
+        [rosterGrade]:
+          rosterGrade === grade
+            ? addUniqueValue(newRoster[rosterGrade], name).sort()
+            : newRoster[rosterGrade].filter((n) => n !== name),
+      }),
+      this._roster
+    );
+  }
+
+  grade(grade: number): string[] {
+    return this.roster()[grade] || [];
+  }
+}