Déjà Vu

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Thor, the Thunder God is fighting a horde of monsters in a cave. The cave is so narrow that it can be represented as an infinite coordinate line. Monsters are standing in positive integer coordinate points. Thor can cast spells at any integer point while flying. The spell has a blast radius, r. Suppose, Thor has cast a spell at point c. Let some monster’s current coordinate be y, now:

This is a companion discussion topic for the original entry at https://toph.co/p/d-j-vu