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All topics›JavaScript›DP: 1D

Decode Ways

intermediatelayer I7 · DP: 1D5 tests

A message of letters was encoded by mapping 'A' to 1 up to 'Z' to 26 and concatenating the numbers. Given the digit string s, return how many ways it can be decoded back into letters.

  • '12' gives 2: AB (1 2) or L (12)
  • A single digit only decodes if it is 1–9 — a lone '0' is invalid
  • A pair of digits only decodes if it reads 10–26, so leading zeros like '06' are invalid
  • If the string cannot be decoded at all, return 0. The empty string returns 0

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