The Heuristic
This video presents the same text shown beside it, spoken and on screen. It adds nothing the text does not say.
State
A heuristic attaches to each state a quick estimate of the cost still remaining to the goal.
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Straight-line distance is the classic: ignoring roads entirely, the crow's mileage from each Riverbend location to Grandmother's door.
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An estimate is an opinion with a number — its quality decides everything downstream.