Trail free response answer 2010

The Trail problem from the 2010 AP Computer Science Exam is typical of free response problems that test arrays. The problem requires you to find the minimum and maximum in an part of an array and access 2 elements of an array for each loop run.

Trail is #3 from the 2010 AP Computer Science Free Response.

https://secure-media.collegeboard.org/apc/ap10_frq_computer_science_a.pdf

Part (a) isLevelTrailSegment method

public boolean isLevelTrailSegment(int start, int end)
{
    int minElevation = markers[start];
    int maxElevation = markers[start];

    for (int i = start + 1; i <= end; i++)
    {
        if (markers[i] < minElevation)
            minElevation = markers[i];

        if (markers[i] > maxElevation)
            maxElevation = markers[i];
    }

    return maxElevation - minElevation <= 10;
}

This is a find the min/max (both in this case) problem with the constraint that only the values at indexes from start up to and including end are considered. The algorithm is the same as any other find the max/min problem.

Part (b) isDifficult method

public boolean isDifficult()
{
    int significantChanges = 0;

    for (int i = 1; i < markers.length; i++)
        if (Math.abs(markers[i - 1] - markers[i]) >= 30)
            significantChanges++;

    return significantChanges >= 3;
}

2010 AP CS Exam Free Response Solutions

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