Infrastructure/Module 12: Algorithm Patterns/12.6
SECTION 12.6

Practice Strategy

How to Learn Patterns

  1. Recognize the pattern — Read the problem, identify which pattern applies
  2. Write the skeleton — Set up the data structure (map, two pointers, window)
  3. Fill in the logic — The invariant that defines your solution
  4. Verify with examples — Walk through with small inputs

Pattern Recognition Cheat Sheet

Signal in Problem Try This Pattern
"Find pair that sums to X" Hash map or two pointers (if sorted)
"Count occurrences" Hash map frequency counting
"Longest subarray with condition" Sliding window
"Find in sorted data" Binary search
"Matching/nesting" Stack
"Minimum needed to satisfy" Binary search on answer
"Merge sorted inputs" Two pointers
"Next greater/smaller element" Monotonic stack

Interview Mindset

  1. State the pattern before coding: "This is a sliding window problem because..."
  2. Start with brute force, then optimize: "Brute force is O(n²), but with a map we get O(n)"
  3. Think out loud — interviewers care about your reasoning, not just the answer
  4. Test edge cases: empty input, single element, all same values
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