= Solution
A <SMILES string> encodes a molecular <graph> as a sequence of atom and bond symbols, with parentheses for branches, matching digits for ring closures and additional symbols for charges and <stereochemistry>. For example,
``
CCO
``
specifies ethanol. A <molecule> may have several valid SMILES traversals, so the raw character sequence is not itself a unique physical descriptor.
Two numerical encodings are:
* A <molecular fingerprint>: a fixed-length vector indicating local substructures, for example hashed circular neighborhoods around atoms. Each coordinate is a bit or a count. The same atom–bond graph should produce the same fingerprint regardless of its SMILES traversal.
* A <molecular descriptor> vector: real-valued quantities such as <molar mass>, atom counts, formal charge, <hydrogen bond donor> and <hydrogen bond acceptor> counts, or topological indices. Standardize these coordinates using the training set before fitting a scale-sensitive model.
These are chemical-structure representations. No biological mechanism is needed to encode the <molecules> or treat the supplied target as a binary label.
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