`WeatherData`

free response problem from the 2023 AP Computer Science A Exam

`WeatherData`

is #3 from the from the 2023 AP Computer Science A Free Response problems.

https://apcentral.collegeboard.org/media/pdf/ap23-frq-comp-sci-a.pdf

## Part (a) `cleanData`

method

```
public void cleanData(double lower, double upper)
{
int i = 0;
while(i < temperatures.size())
{
Double t = temperatures.get(i);
if(t.compareTo(lower) < 0 || t.compareTo(upper) > 0)
temperatures.remove(i);
else
i++;
}
}
```

The use of `compareTo`

is optional. Java will automatically unbox the `Double`

objects into `double`

.

## Part (b) `longestHeatWave`

method (original solution)

```
public int longestHeatWave(double threshold)
{
int almostCurrentLength = 0;
int almostMaxLength = 0;
for(int i = 1; i < temperatures.size(); i++)
{
Double before = temperatures.get(i - 1);
Double current = temperatures.get(i);
if(before.compareTo(threshold) > 0 &&
current.compareTo(threshold) > 0)
{
// in heatwave
almostCurrentLength++;
if(almostCurrentLength > almostMaxLength)
almostMaxLength = almostCurrentLength;
}
else
almostCurrentLength = 0;
}
return almostMaxLength + 1;
}
```

`almostCurrentLength`

stores 1 less than the length of the heatwave that includes the element at `i`

, or `0`

if the element at `i`

is not the second or subsequent element of a heatwave. (`almostCurrentLength`

excludes the first element of the heatwave.)

`almostMaxLength`

stores 1 less than the length of the longest known heatwave, or `0`

if a heatwave has not yet been encountered.

This is a variation of find the minimum or maximum. `almostMaxLength`

starts at `0`

because no heatwave has yet been encountered. (It is also possible to start `almostMaxLength`

at `1`

since the problem description guarantees at least 1 heatwave.) The length of each heatwave encountered is compared against the length of the longest known heatwave.

When I originally approached this problem, I thought of it as being similar to the NumberCube `getLongestRun`

method. My original solution to `longestHeatWave`

is based on updating `almostCurrentLength`

if and only if the value at `i`

is part of a heatwave. This requires comparing consecutive elements and addressing skipping the first element of each heatwave. The additional solution below is more straightforward.

## Part (b) `longestHeatWave`

method (additional solution)

```
public int longestHeatWave(double threshold)
{
int hotInARow = 0;
int maxHotInARow = 0;
for(int i = 0; i < temperatures.size(); i++)
{
if(temperatures.get(i).compareTo(threshold) > 0)
{
hotInARow++;
if(hotInARow > maxHotInARow)
maxHotInARow = hotInARow;
}
else
hotInARow = 0;
}
return maxHotInARow;
}
```

As others (too many to credit) have pointed out, it is not necessary to compare consecutive elements within a single run of the loop. This solution finds the length of the longest run of days that exceed `threshold`

, even if that length is 0 or 1. The problem guarantees that at least 1 heatwave exists, so the length of the longest run will always be `>= 2`

.

Mistake? Please comment below.

## Java files with test code

ThreeTest.java includes JUnit test code with the examples from the problem and 1 additional easily missed example (longest heatwave is at the end).

WeatherData.java

ThreeTest.java

## Additional resources

## 2023 AP CS Exam Free Response Solutions

- AppointmentBook Free Response Solution
- Sign Free Response Solution
- BoxOfCandy Free Response Solution