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Solving the Sum of Two Digits Programming Challenge (screencast)

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Algorithmic Toolbox

Université de Californie à San Diego

4.7 (4,770 notes) | 150K étudiants inscrits

Cours 1 de 6 dans Structures de données et algorithmes Spécialisation

The course covers basic algorithmic techniques and ideas for computational problems arising frequently in practical applications: sorting and searching, divide and conquer, greedy algorithms, dynamic programming. We will learn a lot of theory: how to sort data and how it helps for searching; how to break a large problem into pieces and solve them recursively; when it makes sense to proceed greedily; how dynamic programming is used in genomic studies. You will practice solving computational problems, designing new algorithms, and implementing solutions efficiently (so that they run in less than a second).

Visualiser le programme de cours

Compétences que vous apprendrez

Dynamic Programming, Debugging, Software Testing, Algorithms, Computer Programming

Avis

4.7 (4,770 notes)

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MB

Mar 06, 2018

Cool course. Thank you! One suggestion about your book (Learning Algorithms Through Programming and Puzzle Solving): could you add some theory which would serve as a brief reminder before problems?

PR

Feb 10, 2019

The course is perfectly designed. The perfect start for those who start with data structures and algorithms. The Dynamic programming was a little bit tough but overall course is perfectly designed

À partir de la leçon

Programming Challenges

Welcome to the first module of Data Structures and Algorithms! Here we will provide an overview of where algorithms and data structures are used (hint: everywhere) and walk you through a few sample programming challenges. The programming challenges represent an important (and often the most difficult!) part of this specialization because the only way to fully understand an algorithm is to implement it. Writing correct and efficient programs is hard; please don’t be surprised if they don’t work as you planned—our first programs did not work either! We will help you on your journey through the specialization by showing how to implement your first programming challenges. We will also introduce testing techniques that will help increase your chances of passing assignments on your first attempt. In case your program does not work as intended, we will show how to fix it, even if you don’t yet know which test your implementation is failing on.

Solving the Sum of Two Digits Programming Challenge (screencast)6:30

Enseigné par

Alexander S. Kulikov
Visiting Professor
Michael Levin
Lecturer
Neil Rhodes
Adjunct Faculty
Pavel Pevzner
Professor
Daniel M Kane
Assistant Professor

Transcription

Hi, in this short video, we will solve a code problem together.

The problem itself is quite elementary.

So the main purpose of this video is to show you the general pipeline

of solving code problems in this class.

The problem is called A plus B.

In this problem, we are given two digits on the standard input and

our goal is to output their sum on the standard output.

You can see two sample tests here on the page.

For example, if the input for your program consists of the integers 3 and

2, then your program should output 5.

If, on the other hand, the input consists of two integers 7 and

9, then your program is supposed to output 16, of course.

The next section consists of three Starter files.

Which in this particular case are actually solutions, not just starter files.

So the files are for programming languages Python, Java, and C++.

Finally the last section contains an instruction

consisting of four steps on how to solve this problem.

So let's go through these four steps together.

The first step is to download one of the starter files.

For this, let's select the C++ starter file, and let's download it.

Okay.

Now the file is here and let's take a look inside.

So, this is a very simple solution which, first, creates three variables.

Then it reads a and b from the standard input.

Then it computes the sum.

And then finally it outputs the sum on the standard output.

So to run this program we first need to compile it.

So this is the second step of our instruction.

For this we highly recommend to use the same

compiler flags that are shown on this page.

This will ensure that your program behaves in the same way

on the testing system and on your local machine.

So in this case let's just copy the flags and

use it to compile our program.

So this produced an executable file a.out and we can now run it.

Let's give this program for example 2 and 3.

So the output is 5.

Well, one more test.

9 and 4, the output is 13 as expected.

So far, so good.

And now the next step is to actually submit this solution to this problem.

Let's go to my submission tab.

Press create submission, then replace a file by this .cpp file

And press the Submit button.

So after a while, the testing system shows

that our solution passed all the tests, which is quite satisfactory.

In this particular case, the grader output is empty,

meaning that there is no error message in this case.

To illustrate it one more time, let me repeat the whole procedure quickly for

the Python programming language.

So we first download the starter Python file.

Let's take a look at what is inside.

So the program is again very simple as expected.

So we just take a and be from the standard input and we output the sum of a and b.

Now we need to run this program for

this you might want to go to this available programming languages page.

Again just to check how we run Python scripts so

we just use Python, Python 3.

So let's do this.

For example 4, 4 and the output is 8 which is as expected.

So let's just go ahead and submit this solution.

So you go to the my submission tab, you press the Create Submission button and

then you replace this file by APlusB.py.

So when the file is uploaded, you finally press the Submit button.

So in a few seconds, this solution will be accepted by the testing system.

Well this wasn't very challenging, right?

In the next video we will see a much more

interesting example of a computational problem.

For this problem we will start with a naive solution.

We will submit this solution to a testing system to figure out that it is buggy

actually.

That there is a bug.

So we will fix this bug, submit it again, to find out that our solution is slow.

We will get a time limit exceeded feedback message from the testing system.

Meaning that for large data sets it works in more than one second, for example.

So this will require us to come up with a much, more faster solution.

We will implement it, submit it to the system,

again, to find out that it is still buggy.

We will use stress testing to locate the bug, to fix it, and

to finally submit a correct solution to the system which will pass all the tests.

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