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📜 WAYPOINT LESSON

Fusion mechanisms

⭐⭐⭐ advanced⏳ 10 min read📍 Lesson 202 of 256

String scan plus char arithmetic, list-of-arrays with per-row resets, log processing with a surviving accumulator.

Fusion problems stack two mechanisms where each alone is easy:

  • String scan + char arithmetic: shift vowels only — classify ("aeiou".indexOf(ch) >= 0) then transform (ch + 1). Both halves are intro-level; the fusion is where care lives.
  • List of arrays + per-row analysis: ArrayList<int[]> where each row needs its own max/sum scan — nested loops with a reset between rows. Forgetting the reset is the classic bug.
  • Log processing + running state: walk characters, maintain an altitude/count, answer from the final state. The state variable must survive the whole loop — declaring it inside is the classic bug.

When two mechanisms fuse, write each as a helper if the spec allows, or as clearly separated passes if it doesn't. Fusion is a reading skill; the code stays ordinary.