CP.

Be gin()
Coding Club, IIT Guwahati

>>> Week 1 <<<

*Join the discord server for clearing all your doubts

What is Competitive Programming or CP

You are given a set of problems and you have to solve these problems
in a fixed time
After solving, depending on your rank/percentile you will be awarded
some virtual points.

Why should you do it

Mainly because it’s competitive and programming :
The Competitive part gives you a feel of sports and the Programming
part might help you in your future courses, internships, and
placements.

CONTENTS
Prerequisites (Expected Time: 1-2 days
Resources
Website
Competitions
Implementation (Expected Time: 1 day
STL (Expected Time: 1-2 days
Maths (Expected Time: 0-1 days
AD-HOC (Expected Time: 0-1 days)

PREREQUISITES (Expected Time: 1-2 days)

For this course, there are no prerequisites as such. But to start CP you will
need a decent level of knowledge of at least one programming language
General Order of Preference:-

C++ > Java > Python > Other

It isn’t that tough to switch between languages if you have a hold of at
least one language
We recommend you start with C++ if it is going to be your first
programming language.

If you already have knowledge of Python, we have linked resources for CP

in python, so you can continue with the course. However, we recommend
to learn C++ along the way as it’s better for more difficult problems and
will help you in your college curriculum as well.

SETTING UP AN IDE (Integrated Development

Environment)
In simple words, an IDE is an environment that you will be using to write
your code, compile it and view the output. A suitable and well-equipped
IDE is very important, and not setting it up in the right way may cause
trouble in the future.

(you may spend days fixing it).

Two of the most popular ones are:

VS Cod
Window
Ma
Sublime Text

Don’t mess up while setting it up otherwise you will easily waste days
fixing it!!

STARTING WITH YOUR FIRST PROGRAMMING

LANGUAGE
What we are going to recommend is the fastest and preferred way to
learn C++ / Python. These are short videos, yet they are more than
sufficient.

Resources for C+
Bucky’s Tutorial: Watch lectures 1 to 41 and 71 to 73.

Resources for Pytho

Programming with Mosh: Watching the first three hours would be
sufficient
Corey Schafer - STL

Solve the First 10-20 problems from hackerrank just to get comfortable
with the language you chose.

Note: Do not waste much of your time learning the language ( getting
into tiny details).

TOOLS FOR COMPETITIVE PROGRAMMING

Note: You don’t need to set these up to begin with CP, however, along the
way these tools become really helpful to your journey. You may revisit this
when you get comfortable with CP

VS Code extensions:

To install these extensions, look for the “Extensions” button on the left

sidebar. Then you can search for and install the

Code Runner: With this, you can directly run the code without
having to compile in the terminal .
 Competitive Programming Helper: It automatically reads test

cases from the website which you won’t have to write again and

again. To work with this you also have to install the Competitive

Companion Chrome extension .

2. Sublime Text Packages:

Similar to the cph extension in VS Code, you can find

FastOlympicCoding in Sublime which works with Competitive

Companion .

3. User Code Snippets/Template code:

These are reusable code pieces that can help you avoid re-writing the

same code. You can make them in both VS Code and Sublime Text.

4. Header Files

Including all libraries required can be a tedious task. So we prefer

including <bits/stdc++.h> file instead, which already contains all the

libraries. It is not used in usual C++ codes as it takes a long time to

compile. However, that is not important in CP. It is available from

C++14 and above and it is not directly available for Mac users.

Mac users can refer this video. The folder with include files may not

be the same. To find that, you can make a C++ file, type

#include <iostream> and Ctrl + Click on it to see the file location.

RESOURCES
Handbook (CPH):- You can find 90% of the things you want to learn in
this book, but reading this book completely and then starting to solve
problems is not recommended. Just refer to the book when you come
across a topic that you haven’t heard about before
CSES:- The author of the Handbook has also made a compilation of
300 really good and conceptual problems which covers almost all CP
topics. But it doesn’t contain problems sorted according to difficulty so
you will have to estimate it using solve count
USACO Guide:- This is literally the “one-stop shop”. This website is
generally referred to as USA computing Olympiad aspirants and it has
everything in sorted order. And it has divisions like Bronze, Silver, and
Gold. It will mostly refer to the Handbook and explain solutions to
CSES problems as well
CP-Algorithms:- Contains all CP topics but again not in sorted order of
difficulty. So, refer to it only if you are stuck on a topic and couldn’t find
it in the Handbook
WEBSITES
Some websites from where you can learn and compete and some
important competitions

Codeforces:- Most popular and widely used platform

Contests are mainly of the following types:- Div 4, Div 3, Div 2, Div 1,
Div 1+2, Educational Rounds, and Global Rounds
We recommend participating in all rounds without worrying about
rating changes(ratings are temporary but the experience is unique)
Do try to solve all the problems whose ratings are <= your rating +
300. If you are not able to solve the problems, refer to their editorial.
If you still don’t understand the solution, discuss it with your friends
or ask your doubts in the competitive-programming-discussion
channel on our Discord
Atcoder:- Educational and Weekly contests with quality problems
3 types of contests:- Atcoder Beginner/Regular/Grand contes
Must participate in Atcoder Beginner Contests (100 mins a week
isn’t that much
Codechef:
Monthly contests:- Long challenge and Lunch-tim
Weekly contests named starters

It is highly recommended to start giving contests regularly once you have

some basic knowledge about cp.

IMPORTANT YEARLY COMPETITIONS

* We will send you a reminder before all these contests when to participate

Google Contests:- Don’t miss any of them unless you have an exam at
the same time
Google Kickstart:
8 times a year. All 8 contests are independent
Sometimes the problems are irritating but still, it's a google
contest
Google Codejam:
Held once a year. Probably the biggest CP contest
5 rounds in increasing order of difficulty, with elimination in each
Round
Prelims->Round A->Round B->Round C-> world final
Google Hashcode:
Held once a year and is very different from normal CP contests
You have to come up with a solution to a problem and improve it
to gain more points. Problems couldn’t be solved completely
Meta HackerCup:- It is also a once-a-year contest in topological order
just like Google Code Jam
ACM ICPC:- Held once a year and the Biggest CP contest for college
students. Also in topological order
Online -> Regionals -> World Final
Codechef SnackDown:- Held once every two years. The Next will be in
2023.

IMPLEMENTATION
(Expected Time: 1 day)
After we have learned a language, we can now get started with actual
problem-solving.

Problem-solving requires understanding the problem statement and

designing an effective algorithm that successfully solves the task at hand.

The efficiency of algorithms is very important in competitive

programming. Usually, it is easy to design an algorithm that solves the
problem slowly, but the real challenge is to invent a fast algorithm. If the
algorithm is too slow, it will get only partial points or no points at all.

Thus comes into the picture the concept of time complexity. By

calculating the time complexity, we can find out whether the algorithm is
fast enough without implementing it.

Here are some resources which will help you understand time
complexity: -

1. CPH (Competitive Programmers’ Handbook) Chapter 2

Do read this chapter thoroughly without skipping to get a complete
understanding of Big O notation etc.

2. Big-O notation in 5 minutes

3. This blog might help you in avoiding Time Limit Exceeded error

Some more aspects of a language become handy while doing CP

problems. One such aspect, which we usually ignore when learning the
language is that of range of numbers.

In Python3, the int type stores large enough numbers, so you don’t have
to worry about the value which will be stored in the variable.
In C++, int is a data type that takes up 32 bit of space and can store
integers ranging from -2,147,483,648 to 2,147,483,647. However, the
answers in the problems very often go over that range and give wrong
output. This is called integer overflow. Hence, we can use long long data
type over int in such cases. You can read more about it here. This can be
really frustrating if not taken care of as the code gives wrong output even
when your approach is correct.

Following are some challenging problems based mainly on

implementation:

Increasing Array (Solution

Permutations (Solution
Number Spiral (Solution
Chloe and the sequence (Solution
Viki and Squares (Solution
Trailing Zeroes (Solution
Masha and two friends (Solution)

*Try to attempt a question for a minimum of 30 minutes before checking

the solution.

*We have attached the codes with solutions. If you still have any doubts
feel free to ask us in the discord channel.

*In general, the solutions to the problems can be found in the Editorial/
Tutorial section on websites like Codeforces, Atcoder etc. For CSES, most
of the solutions can be found on google.

STL (Expected Time: 1-2 days)

The Standard Template Library (STL) is a set of C++ template classes to

provide common programming data structures and functions such as
lists, stacks, arrays, etc.

At the core of the C++ Standard Template Library are the following three
well-structured components − containers, algorithms, and iterators.
Basic knowledge of STL is quite handy, and in fact, necessary for
competitive programming.

Resources

Standard Template Library in C++ - Great Learnin

The C++ Standard Template Library (STL) - GeeksforGeek
Watch this video to learn the basics of ST
Read Ch-4 of CPH (pg 35-pg 43)

Frequently used containers

Array: Arrays are used to store multiple values in a single variable,

instead of declaring separate variables for each value. Vector is used
more frequently compared to array since the former is dynamic in
nature. However, higher dimensional arrays are simpler to declare
than vectors

Vector: One of the most powerful and frequently used STL containers.
Vectors are the same as dynamic arrays with the ability to resize
themselves automatically when an element is inserted or deleted.
Study these functions only:

push_back(), pop_back(), sort(), upper_bound()* , lower_bound()* ,

begin(), end(), rbegin(), size(), resize(), accumulate(), binary_search()*

clear() and find()*.

 Pair: Pair is a container that contains two values. It is used to combine

two values and associate them even if they are of different types. The
first and second values of a pair ‘p’ can be accessed using p.first and
p.second

Set: A container that keeps a unique copy of every element in sorted

order. Study these functions only:

insert(), erase(), begin(), end(), rbegin(), size(), lower_bound(),

upper_bound(), find() and clear(

Multiset: Similar to a set, but it can also store multiple copies of an

element

Map: Maps are containers that store elements in a mapped fashion.

Each element has a key value and a mapped value. Study these
functions only:

insert(), erase(), begin(), end(), rbegin(), find(), clear(), size()

lower_bound(), upper_bound(), and the operator []

*The use of these containers and their functions will be explained in the
upcoming weeks

Not-so-frequently used containers

Stack: Stacks are a type of container adaptor that operate in a Last In

First Out (LIFO) type of arrangement. Elements are added at one end
(top) and are removed from that end only

Queue: Queues are a type of container that operates in a First In First

Out (FIFO) type of arrangement, unlike Stack. Elements are inserted at
the back (end) and are deleted from the front

Priority Queue: Priority queues are queues such that the first element
is either the greatest or the smallest of all elements in the queue and
elements are in nonincreasing order.

 Deque: Double-ended queues are a special case of queues where

insertion and deletion operations are possible at both end
MultiMap: Multimap is similar to a map with the addition that
multiple elements can have the same keys

STL EQUIVALENT IN PYTHON

Frequently used containers
List: Lists are used to store multiple values(they may not be of the
same data type) in a single variable, instead of declaring separate
variables for each value
Dictionary: It is equivalent to an unordered map of C++ STL. Maps are
containers that store elements in a mapped fashion. Each element
has a key value and a mapped value. It does not store elements in a
sorted manner like C++ Map.

Sets: A set is an unordered collection of items. Every set element is

unique (no duplicates). Sets can also be used to perform
mathematical set operations like union, intersection, etc.

Some more containers

Deque: It can be used to implement queue and deque similar to
those given in C++ STL
Heapq: The property of this data structure is that each time the

smallest heap element is popped. It is the python equivalent of a

priority queue.

Frequently used Modules

Math: It contains all the basic Math operations ranging from ceil, and
floor to factorial, pow, etc

Sys: It’s generally used for some specific functions revolving around
the std input and output. Eg: sys.stdin.readline() (which takes input
faster than the normal input function), sys.stdout.flush() (used in
interactive problems) , sys.setrecursionlimit(int) (to increase the
recursion limit) , et

Bisect: Has 2 functions, bisect_right(list, key) which finds and returns

the index of the minimum element in the list greater than the key,
and bisect_left(list, key) which finds and returns the index of the
maximum element in the list lesser than key both in O(log(len(list))
complexity

Random: Has its use in some of the probability-based questions and in

question generation. Some common functions of random:
Random.randint(a,b) which generates a random integer between a

and b .

Random.shuffle(list) returns a shuffled version of a given list in

O(len(list)) .

Following are some practice problems:

Distinct Numbers (C++Solution) (Python-soln

Remove Duplicates (C++Solution) (Python-soln
Registration System (C++Solution) (Python-soln
T-Shirt Buying? (C++Solution) (Python-soln
Subarray Sums (C++Solution)(Python-soln
Scope (C++Solution)(Python-soln
Movie Festival (C++Solution) (Python-soln)
MATHS

(Expected Time: 0-1 days)

There are several questions in CP, which can be solved only by

observations and logical reasoning skills. No algorithm is needed as such
to solve these kinds of problems. Such questions test the intuitive/
mathematical skills of the programmer, and not his/her coding skills.

Try to solve these given problems without using any known algorithms:-

Little Elephan
Hard Calculatio
Who's Opposit
Comma
Additional Questions for practice
Histogram Uglines
Pythagorean Triple
Fraction Floor Su
Cat Cycle

AD-HOC PROBLEMS

(Expected Time: 0-1 days)

Ad hoc problems are those whose algorithms do not fall into standard
categories with well-studied solutions. There are no general techniques to
solve them. They are intuition-based problems, and you may understand
better by solving these:

Teleportatio
Funny Permutatio
Three Door
Sleepy Cow Herding

Additional Questions for Practice

Exchang
Do you know your ABCs
Sleepy Cow Sortin
Difference of GCDs