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Fenwick tree or binary indexed tree allows us to answer range queries like prefix sums, but also while performing point updates, i.e., changing some value in our data. It is much simpler and faster than its brother - segment tree, though not as flexible. In this class, we are going to look at how it works by using it in some problems.

Fenwick Tree and problem solving

Segment Trees & BIT

This is the official video editorial of the CodeChef February Lunchtime 2021 problem, Minimum Divisibility Set  (Problem Code : MDIVSET), which was kept as the second hardest problem in Division 1.

Minimum Divisibility Set (MDIVSET) | February Lunchtime 2021

Advance Graph Algorithms

Chinese Remainder Theorem, commonly known as CRT, is a very powerful tool in number theory which is also required in many competitive programming problems. In this one hour session, we are going to study CRT in its entirety and look at some problems.

Chinese Remainder Theorem

Advanced Number Theory

Modulo arithmetic is a very well known topic in competitive programming. Many problem authors assume that participants already know about this. In this onw hour session, we are going to discuss this topic until modulo inverse.

Modulo Arithmetic

Number Theory

In this session, we will look at what is MO's algorithm, which is a popular algorithm in the squareroot decomposition paradigm.  We will discuss when it can be applied and also solve a couple of problems based on it.

MO's algorithm - theory and problem solving

Square Root Decomposition

Prime numbers play a central role in almost all problems in number theory. In this session, we are going to look at how to find out if a number is prime or composite, a domain of algorithms known as primality tests.

Primality tests - finding if a number is prime

This is the official video editorial of the CodeChef January Lunchtime 2021 problem, Random Grouping (Problem Code : EXPGROUP), which was kept as the hardest problem in Division 1.

Random Grouping (EXPGROUP) | January Lunchtime 2021

In this session, we will discuss the harder problems of https://www.codechef.com/ICPCTR04, which is a mirror of ICPC 2016, Indian online preliminary round (ACMIND16). See https://www.codechef.com/icpc/training-series for more details

AIM-ICPC | Contest 4 | Lecture 3

Expert Data Structures

This is the 5th class in the micro course "FFT in Polynomial operations and Advanced Combinatorics". In this class, we are going to be using many different concepts we learned in the previous classes, like how to solve convulutions, how to compute Stirling numbers of the first kind, and how to do multipoint evaluation of a polynomial, to finally see how do we calculate something as simple as 1 x 2 x 3 x ... x n in less than O(n) time.

Factorial of a large number

Advanced Combinatorics

This is the 4th class in the micro course "FFT in Polynomial operations and Advanced Combinatorics". In this class, we are first going to look at what does stirling number of first kind actually means, and how can it be used in various combinatoric problems. We are also going to be looking at many different properties surrounding it. Then we are going to use the knowledge of solving convolutions from FFT that we learned in the previous class, to efficiently compute these numbers.

Stirling numbers of First kind

In this class we are going to see a special optimization in Dynamic Programming, called Divide and Conquer DP. This method utilizes the divide and conquer paradigm to find the optimal values of dp faster. We are also going to solve problems based on this concept.

Divide and Conquer DP

Advanced Dynamic Programming

In this class, we are going to see how to factorize a number in cube root time, as opposed to the normal square root time taken. This method sacrifices some information in order to bring the time complexity down. We are then going to solve problems based on this concept

Factorization of a number in cube root time

Legend

Master

Star

Rising Star

India

Indian Institute of Technology, Guwahati

Bhopal, Madhya Pradesh, India

Codechef : Seven Star & Codeforces : International Grandmaster 
& Codejam 2020 : Until round 3 and secured rank 267th globally & Kickstart 2020 : Got global ranks 21st in round C and 26th in round D

Sensational! We are proud to call you an Unacademy veteran. Onwards and upwards!

10k minutes

Your perseverance is inspirational. Cherish this huge moment, you’ve earned it!

5k minutes

Woohoo! You’re officially a learning rockstar. Keep racking up more thousands!

1000 minutes

You deserve this honour for all the hard work! 500 is a big milestone. Keep going higher and faster!

500 minutes

Your first century, you did it! Go ahead, tell the world. 

100 minutes

Woot! You're halfway to a century of learning minutes. Keep going strong!

50 minutes

Congratulations on your first learning milestone! Here's to many more in the future. 

Nishchay Manwani

Ex-Educator

Fenwick Tree and problem solving

Minimum Divisibility Set (MDIVSET) | February Lunchtime 2021

Chinese Remainder Theorem

Modulo Arithmetic

MO's algorithm - theory and problem solving

Primality tests - finding if a number is prime

Random Grouping (EXPGROUP) | January Lunchtime 2021

AIM-ICPC | Contest 4 | Lecture 3

Factorial of a large number

Stirling numbers of First kind

Divide and Conquer DP

Factorization of a number in cube root time

Nishchay Manwani

Ex-Educator .css-1icgrfo-StyledTypography{font-weight:600;text-transform:initial;}.css-kc26im-StyledTypography{margin:0;color:var(--color-text-secondary);font-weight:600;text-transform:initial;}

Fenwick Tree and problem solving

Minimum Divisibility Set (MDIVSET) | February Lunchtime 2021

Chinese Remainder Theorem

Modulo Arithmetic

MO's algorithm - theory and problem solving

Primality tests - finding if a number is prime

Random Grouping (EXPGROUP) | January Lunchtime 2021

AIM-ICPC | Contest 4 | Lecture 3

Factorial of a large number

Stirling numbers of First kind

Divide and Conquer DP

Factorization of a number in cube root time

Ex-Educator