The FuelDepot problem from the 2011 AP Computer Science Exam is typical of free response problems that test lists.

FuelDepot is #3 from the from the 2011 AP Computer Science A Free Response problems.

Part (a) nextTankToFill method

public int nextTankToFill(int threshold)
    int tankWithLeast = 0;

    for (int i = 1; i < tanks.size(); i++)
        if (tanks.get(i).getFuelLevel() < tanks.get(tankWithLeast).getFuelLevel())
            tankWithLeast = i;

    if (tanks.get(tankWithLeast).getFuelLevel() <= threshold)
        return tankWithLeast;
        return filler.getCurrentIndex();

This is a standard find the min problem with a minor twist (the threshold). The code above handles finding the minimum first then handles the comparison with threshold at the end.

This problem can also be solved by initializing tankWithLeast to filler.getCurrentIndex() and checking the threshold as part of finding the minimum. (The alternate approach has the benefit of working even with 0 tanks, though it is not clear where the robot would be if there were 0 tanks.)

Part (b) moveToLocation method

public void moveToLocation(int locIndex)
    if (locIndex == filler.getCurrentIndex())

    if ((locIndex < filler.getCurrentIndex() && filler.isFacingRight())
            || (locIndex > filler.getCurrentIndex() && !filler.isFacingRight()))

    filler.moveForward(Math.abs(locIndex - filler.getCurrentIndex()));

2011 AP CS Exam Free Response Solutions

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