## DEV Community is a community of 906,671 amazing developers

We're a place where coders share, stay up-to-date and grow their careers. Well, the goal is that we to solve 25 programming challenges to get a star and get better at out job.

# Part One

In the first challenge (Sonar Sweep), as the submarine descends, a series of numvers appear on the screen that are the input of out puzzle.

We need to find all the numvers that are greater than the previous number.Usually the first numver does not count because the first number does not have previous number.

``````* 199 (N/A - no previous number)
+ 200 (increased)
+ 208 (increased)
+ 210 (increased)
- 200 (decreased)
+ 207 (increased)
+ 240 (increased)
+ 269 (increased)
- 260 (decreased)
+ 263 (increased)
``````

In this example, the answer is `7`, because the are seven numbers that have icreased compared to the previous number.

After reveiving the input file, we go to solve problem using a programming language.Of course, you can also count these manually:)

Here we use Python

The first step is for us to read the input of the puzzle and clear its data.

‍‍

``````with open("input.txt") as f:
numbers = [int(i.strip()) for i in lines]
``````

#### Iterate on data and calculating it

The next step is iterate on data with `for` loop or any method we we can and see if it has increased or not.

``````# create a variable containing the first number for first itration
prev_num = numbers[-1]

# on start result is 0
result = 0

for i in numbers:
# check if the previous value is lower than the current value, increase count by 1
if i > prev_num:
result += 1

# update the prev_num for the next iteration
prev_num = i

print(f"[ part1: {result} ]")
``````

# Part Two

It is now said:

Considering every single measurment isn't as useful as you expected: ther's just too much noise in the data. Instead, consider sums of a three-measurment sliding window.

‍‍‍‍

``````199  A
200  A B
208  A B C
210    B C D
200  E   C D
207  E F   D
240  E F G
269    F G H
260      G H
263        H
``````

That means we have to add the numbers three by three and then compare them.

``````A: 607 (N/A - no previous sum)
B: 618 (increased)
C: 618 (no change)
D: 617 (decreased)
E: 647 (increased)
F: 716 (increased)
G: 769 (increased)
H: 792 (increased)
``````

In this example, the answer is `5`.

Now let's go on to writing a programe for this.

``````# on start result is 0
result = 0

size = len(numbers)

# create a variable containing the sum of the first three-measurement sliding window
prev_window = sum(numbers[:3])

# iterate over the size of the depths file
for i in range(3, size):
# calculate the current three-measurement sliding window
curr_window = prev_window + numbers[i] - numbers[i-3]

# check if the previous value is lower than the current value, increase count by 1
if prev_window < curr_window:
result += 1

# update the prev_window for the next iteration
prev_window = curr_window

print(f"[ part2: {result} ]")
``````

Goodbye :)