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Finite-State Parsing and Digit Carry Handling

Problem

When you see digits as arrays or strings, manual parsing, carry, overflow, sign, clamp, or "implement what the language already does"

Strategy: Finite-State Parsing and Digit Carry Handling

  • Think about this
    • Treat it as a finite-state scan:
      • skip prefix
      • read optional sign
      • accumulate digits
      • stop on first invalid char
    • Build the numeric answer incrementally and check overflow before multiplying by 10.
    • For digit arrays, think right-to-left carry propagation.
  • Avoid this
    • Do not convert giant substrings to int if overflow handling is the point.
    • Do not call strip() when only leading spaces are allowed to be ignored.
    • Do not forget the all-9 case or "sign with no digits" case.
  • Tell this to the interviewer
    • Describe the parser states in order.
    • Say the overflow guard before writing the loop.
  • See these problems