Given an array nums (which may contain repeated values) and a target, return the index of the target's first (leftmost) occurrence, or -1 if it does not appear. With duplicates, "where is it?" has several answers, so the question must say which one. The scan directionScan DirectionWhether a loop walks from the first index up or from the last index down — it decides which match is met first. decides which match is seen first: scanning from the left finds the first occurrence immediately, while scanning from the right has to go all the way through.