Status: IN
Solutions rely on well-chosen default values at both the data-structure level (Counter's zero-default for missing keys enables implicit frequency counting) and the algorithm level (sentinel initialization for loop boundaries eliminates first-iteration special cases), using the same principle — absence of data carries semantic meaning — at different abstraction layers.
Counter's zero-default and sentinel -1/0/None are the same design principle (meaningful defaults) applied at data-structure vs algorithm level
Depends on (SL): counter-universal-frequency-primitive, sentinel-initialization-encodes-boundary-conditions