Spaced Repetition Coach

Expert guidance on using spaced repetition effectively for LeetCode interview preparation.

Color-Coding System

The app uses an Anki-style color system to track problem mastery:

Color Progression

• Gray (New): Never attempted or just added
• Orange (Learning): Attempted but need more practice
• Yellow (Reviewing): Getting comfortable, need periodic review
• Green (Mastered): Confident, can solve efficiently

Color Transitions

Moving Forward:

• Gray → Orange: First successful attempt
• Orange → Yellow: Second successful attempt (after waiting period)
• Yellow → Green: Third successful attempt (after longer waiting period)

Moving Backward (Regression):

• If you fail to solve a problem correctly, move it back one color level
• This ensures you focus on problems you're actually struggling with

Eligibility Thresholds

Problems become eligible for review based on color and time since last attempt:

Color	Threshold	Reasoning
Gray	Always eligible	New problems always available
Orange	3+ days	Short interval for recent learning
Yellow	7+ days	Medium interval for consolidation
Green	14+ days	Long interval for maintenance

Key Principle: The better you know a problem, the longer you wait before reviewing it.

Daily Selection Algorithm

The system creates a balanced daily practice set using these ratios:

Selection Ratios

For a typical 5-problem daily session:

• 50% New (Gray): 2-3 problems

  • Keeps you learning new patterns
  • Expands your problem repertoire

• 40% Review (Orange/Yellow): 2 problems

  • Reinforces recent learning
  • Prevents forgetting

• 10% Mastered (Green): 0-1 problem

  • Maintains long-term retention
  • Keeps skills sharp

Example Daily Selection (5 problems)

Day 1:
- 2 Gray (new)
- 2 Orange (review from 3+ days ago)
- 1 Yellow (review from 7+ days ago)

Day 15:
- 3 Gray (new)
- 1 Orange (review)
- 1 Green (maintenance from 14+ days ago)

Optimization Strategies

When You Have Limited Time

3 problems/day (minimum effective dose):

• 2 Gray (new)
• 1 Orange/Yellow (review)

5 problems/day (recommended):

• 3 Gray (new)
• 2 Orange/Yellow (review)

7+ problems/day (intensive prep):

• 3-4 Gray (new)
• 2-3 Orange/Yellow (review)
• 1 Green (maintenance)

When You're Behind on Reviews

If you have many eligible reviews piling up:

1. Prioritize older reviews: Problems waiting longest get selected first
2. Increase daily problem count: Temporarily do 7-10 problems/day
3. Be honest with colors: If you can't solve it, mark it appropriately

When You're Running Out of New Problems

1. Import more problems: Add problems from specific companies or topics
2. Focus on reviews: Increase review ratio temporarily (30% new, 70% review)
3. Reset old greens: Move ancient green problems back to yellow for refresh

How Colors Should Be Assigned

Be honest and strict with yourself:

Gray → Orange

• You solved it with the right approach
• May have needed hints on implementation details
• Understood the solution when complete

Orange → Yellow

• Solved independently without hints
• Identified the correct pattern
• May have been slower than optimal

Yellow → Green

• Solved efficiently in reasonable time
• Optimal time/space complexity
• Can explain the solution clearly
• Would be confident solving in an interview

Regression (Move Back)

• Couldn't remember the approach
• Needed to look up the solution
• Got the wrong pattern entirely
• Took much longer than expected

Advanced Techniques

Pattern-Based Learning

Group problems by pattern and learn them together:

• All sliding window problems in a week
• Then all DP problems the next week
• This reinforces pattern recognition

Interleaving

Mix different patterns in daily practice:

• Better for long-term retention
• Improves pattern recognition
• Mirrors real interview conditions

Deliberate Difficulty

If a color feels too easy:

• Challenge yourself with harder variants
• Set time limits (20-30 minutes)
• Explain solution without code first

Common Mistakes to Avoid

1. Moving Colors Too Quickly

• Don't mark something green just because you solved it once
• Wait the full intervals between attempts
• Be honest about your confidence level

2. Ignoring Reviews

• Don't skip review problems to do only new ones
• Reviews are critical for retention
• Balance is key

3. Gaming the System

• Don't look up solutions and mark as complete
• This defeats the purpose of spaced repetition
• You'll struggle in actual interviews

4. Not Adapting the Schedule

• Adjust daily problem count based on available time
• Scale ratios if you're short on new problems
• Increase reviews before interviews

Measuring Progress

Healthy Metrics

• Green percentage increasing: More problems mastered over time
• Review success rate high: 80%+ of reviews completed without regression
• Pattern recognition improving: Identifying patterns faster
• Time per problem decreasing: Getting more efficient

Warning Signs

• Too many eligible reviews: You're adding problems too fast
• Frequent regressions: Need to wait longer between attempts
• Everything is gray/orange: Not enough consistent practice
• Everything is green: May need harder problems or be marking too generously

Integration with Interview Prep Timeline

3 Months Before Interview

• Focus on new problems (60% new, 40% review)
• Build broad pattern knowledge
• Daily quota: 5-7 problems

1 Month Before Interview

• Balanced approach (50% new, 50% review)
• Solidify weak patterns
• Daily quota: 5-7 problems

2 Weeks Before Interview

• Review-heavy (30% new, 70% review)
• Focus on company-specific patterns
• Daily quota: 5-10 problems

1 Week Before Interview

• Maintenance mode (20% new, 80% review)
• Focus on greens and yellows
• Keep skills sharp
• Daily quota: 3-5 problems

Tips for Maximum Effectiveness

1. Consistency > Intensity: Better to do 3 problems daily than 20 problems once a week
2. Track patterns: Notice which patterns you struggle with
3. Time yourself: Simulate interview pressure
4. Write clean code: Practice interview-quality code, not just working code
5. Explain out loud: Practice verbalizing your approach
6. Review mistakes: Spend time understanding why you got stuck

The Science Behind It

Spaced repetition leverages:

• Spacing Effect: Information is better retained when study sessions are spaced out
• Testing Effect: Active recall strengthens memory more than passive review
• Desirable Difficulty: Slightly challenging reviews optimize learning

The goal is to review each problem just before you would forget it - maximizing retention while minimizing review time.