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Problem & Sheet Architecture Refactoring

Summary of Changes

The problem and sheet management system has been refactored to eliminate redundancy by implementing a proper many-to-many relationship between problems and sheets.

Previous Architecture (Redundant)

  • Each problem had a sheetId field
  • Same problem in multiple sheets = multiple duplicate documents
  • Updating a problem in one sheet didn't update it in others
  • Wasteful database storage

New Architecture (Non-Redundant)

  • Problems exist independently without sheet references
  • SheetProblem junction table manages the many-to-many relationship
  • Same problem can belong to multiple sheets without duplication
  • Single source of truth for each problem

Files Modified

Models

  1. server/models/problem.model.js

    • Removed sheetId and order fields
    • Added unique: true to title field
    • Problems now exist independently

  2. server/models/sheetProblem.model.js ✨ NEW

    • Junction table for many-to-many relationship
    • Fields: sheetId, problemId, order
    • Unique compound index on (sheetId, problemId)

Controllers

  1. server/controllers/problem.controller.js

    • createProblem() - Creates independent problems
    • addProblemToSheet() - Adds existing problem to a sheet
    • removeProblemFromSheet() - Removes from sheet (doesn't delete problem)
    • deleteProblem() - Deletes problem from all sheets
    • markProblemComplete() - Now requires both problemId and sheetId

  2. server/controllers/problemSheet.controller.js

    • Updated deleteProblemSheet() - Deletes SheetProblem relations
    • Updated getSheetProblems() - Uses aggregation with SheetProblem junction
    • Updated getSheetMetrics() - Works with new architecture

Middleware

  1. server/middleware/validateProblem.js
    • Removed order validation (now in SheetProblem)

Scripts

  1. server/scripts/seedBlind75.js ✨ NEW

    • Complete Blind 75 problem set (all 75 problems)
    • Creates problems independently
    • Links them to sheet via SheetProblem

  2. server/scripts/migrateProblemArchitecture.js ✨ NEW

    • Migrates existing data from old to new architecture
    • Includes rollback functionality

How to Use

1. Migrate Existing Data (One-Time)

cd server
node scripts/migrateProblemArchitecture.js

This will:

  • Find all problems with sheetId
  • Create SheetProblem relationships
  • Remove sheetId and order from problems

Rollback (if needed):

node scripts/migrateProblemArchitecture.js --rollback

2. Seed Blind 75 Problems

cd server
node scripts/seedBlind75.js

This creates all 75 Blind 75 problems and the sheet.

Clear Blind 75:

node scripts/seedBlind75.js -d

API Changes

Creating Problems

Old Way:

POST /api/sheets/:sheetId/problems
Body: { title, difficulty, platform, platformLink, order, ... }

New Way:

// Step 1: Create problem independently
POST /api/problems
Body: { title, difficulty, platform, platformLink, ... }

// Step 2: Add to sheet(s)
POST /api/sheets/:sheetId/problems/:problemId
Body: { order: 1 } // optional

Marking Complete

Old Way:

PUT /api/problems/:problemId/complete

New Way:

PUT /api/sheets/:sheetId/problems/:problemId/complete
Body: { completed: true }

Removing from Sheet

// New endpoint - removes problem from sheet WITHOUT deleting it
DELETE /api/sheets/:sheetId/problems/:problemId

Benefits

✅ No Duplication - Each problem stored once
✅ Consistency - Updates propagate to all sheets
✅ Flexibility - Easy to add/remove problems from sheets
✅ Better Data Integrity - Single source of truth
✅ Storage Efficiency - Reduced database size
✅ Maintainability - Easier to manage problems

Database Schema

Problems Collection

{
  _id: ObjectId,
  title: String (unique),
  description: String,
  difficulty: 'easy' | 'medium' | 'hard',
  platform: String,
  platformLink: String,
  tags: [String],
  hints: [{hintNumber, content}],
  solution: {content: {python, javascript, ...}, explanation},
  createdAt: Date,
  updatedAt: Date
}

SheetProblems Collection (Junction)

{
  _id: ObjectId,
  sheetId: ObjectId (ref: ProblemSheet),
  problemId: ObjectId (ref: Problem),
  order: Number,
  notes: String, // Optional sheet-specific notes
  createdAt: Date,
  updatedAt: Date
}

ProblemSheets Collection

{
  _id: ObjectId,
  name: String (unique),
  slug: String,
  description: String,
  icon: String,
  totalProblems: Number,
  isActive: Boolean,
  createdAt: Date,
  updatedAt: Date
}

Blind 75 Problem List

The seed script includes all 75 problems categorized as:

  • Array (10 problems)
  • Binary (5 problems)
  • Dynamic Programming (11 problems)
  • Graph (8 problems)
  • Interval (6 problems)
  • Linked List (6 problems)
  • Matrix (4 problems)
  • String (9 problems)
  • Tree (13 problems)
  • Heap (2 problems)

All problems include:

  • Title, difficulty, platform, platform link
  • Tags for categorization
  • Detailed description

Next Steps

  1. Run Migration - Convert existing data
  2. Seed Blind 75 - Import the complete problem set
  3. Update Frontend - Adjust API calls if needed
  4. Test Thoroughly - Verify all CRUD operations work

For questions or issues, refer to the migration and seed scripts.