Decode the Message — Solution & Editorial

Back to the Problem

DP over positions: extend by a single non-zero digit, or by a two-digit value in [10, 26]. Zeros are the trap — a 0 must attach to a preceding 1 or 2.

Complexity: O(N)

Watch out: Strings like 100 have zero decodings; every 0 needs a valid two-digit partner.