Spaced Repetition for Coding Interviews: Stop Forgetting What You Learn

You solved 200 LeetCode problems. Six months later, you can't remember how to do Two Sum.

Sound familiar? You're not alone. The forgetting curve is brutal, and most interview prep ignores it completely.

The Problem: We Forget Everything

In 1885, psychologist Hermann Ebbinghaus discovered something uncomfortable: without review, we forget 70% of new information within 24 hours.

For coding interviews, this means:

• That clever DP solution you figured out last month? Gone.
• The tree traversal pattern you mastered? Fuzzy at best.
• The 50 problems you grinded before your last interview? Maybe 10 stuck.

Grinding without a retention system is like filling a bucket with holes.

The Solution: Spaced Repetition

Spaced repetition is a study technique that schedules reviews at optimal intervals to maximize retention. Instead of cramming everything once, you review material right before you're about to forget it.

Here's how the forgetting curve changes with spaced review:

Without review:     Day 1: 100% → Day 2: 30% → Day 7: 10%
With spaced review: Day 1: 100% → Day 3: 85% → Day 14: 80% → Day 60: 75%

The magic: each review strengthens the memory, extending the time until the next review is needed.

How Spaced Repetition Works for Coding

The Basic Algorithm (SM-2)

1. Solve a new problem
2. Rate your performance: Easy, Medium, Hard
3. Schedule next review based on difficulty:
   • Hard → Review in 1 day
   • Medium → Review in 3 days
   • Easy → Review in 7+ days
4. Repeat: Each successful review extends the interval

Practical Example

Let's say you learn the "Two Pointers" pattern:

After 5 reviews spread over 45 days, the pattern is locked in long-term memory.

DIY Spaced Repetition Setup

You can build your own system with free tools:

Using Anki (Free)

1. Create a deck for "Coding Patterns"
2. Add cards for each problem/pattern you learn
3. Include:
   • Front: Problem description
   • Back: Key insight, pattern name, time complexity
4. Review daily (10-15 minutes)

Card Example:

Front: "Given an array, find two numbers that add up to target"
Back: "Two Sum - Use a hash map to store complements. O(n) time, O(n) space. Pattern: Hash Map lookup"

Using Notion or Spreadsheet

Create a review schedule:

Update manually after each review.

Downside: Requires discipline and manual tracking.

Automated Spaced Repetition for Code

Manual tracking is tedious. Tools like CodeSparring automate the entire process:

1. Solve a problem → System records your performance
2. Algorithm calculates optimal next review date
3. Dashboard shows what to review today
4. Notifications remind you when patterns are decaying

See your personalized review schedule

What to Put in Your Spaced Repetition System

Don't review every problem. Focus on:

High-Priority (Review Frequently)

• Core patterns: Two Pointers, Sliding Window, BFS/DFS, DP basics
• Problems you struggled with: These need more reinforcement
• Pattern-defining problems: The "canonical" example of each technique

Low-Priority (Review Occasionally)

• Easy problems you ace every time
• Obscure patterns unlikely to appear
• Language-specific tricks

Skip Entirely

• Problems you could do in your sleep
• Highly specialized/rare patterns
• "Gotcha" problems that test tricks rather than understanding

The 15-Minute Daily Review

Here's a sustainable routine:

Morning (15 minutes)

1. Open your spaced repetition tool
2. Review 3-5 problems due today
3. For each problem:
   • Read the problem
   • Recall the key insight (don't look!)
   • Rate your recall: Easy/Medium/Hard
4. Done

Weekly (1 hour)

1. Solve 2-3 new problems
2. Add them to your review system
3. Identify weak patterns to focus on

Common Mistakes

1. Reviewing Solutions Instead of Solving

Don't just read the solution—actually attempt the problem before checking. Passive review doesn't build recall.

2. Too Many Cards/Problems

Start with 20-30 core problems. Quality over quantity. You can add more as these become easy.

3. Skipping Review Days

Consistency beats intensity. 15 minutes daily beats 2 hours on weekends.

4. Not Rating Honestly

If you struggled, mark it "Hard." Your system can only help if you're honest about difficulty.

Does It Actually Work?

Research on spaced repetition for technical learning:

• Medical students using spaced repetition score 50% higher on long-term retention tests
• Language learners retain 90%+ of vocabulary vs 20% with traditional study
• Programmers report significantly better algorithm recall in interviews

The technique isn't new—it's just underused in tech interview prep.

Getting Started Today

Option 1: DIY

1. Download Anki (free)
2. Create cards for the 15 core patterns
3. Review 10 minutes daily

Option 2: Automated

1. Sign up for CodeSparring
2. Complete the assessment
3. Follow your personalized review schedule

Either way, the key is starting and being consistent.

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The Bottom Line

You can grind 500 LeetCode problems and still bomb your interview because you forgot everything.

Or you can learn 50 patterns deeply, review them systematically, and walk into your interview with genuine mastery.

Spaced repetition is the difference between temporary cramming and permanent knowledge. Start using it today.

See which problems you should review today →