Important Tools
Coding Schedule
It is recommended to install both, the browser extension in your PC, as well as the mobile app, from here, to get the notifications of the ongoing contests, regularly.
The On-Line Encyclopedia of Integer Sequences (OEIS)
OEIS has a very huge database of countless integer sequences and patterns. It also features a powerful search engine. Sometimes a seemingly difficult combinatorics problem could be equivalent to a simple integer sequence.
CP Editor
CP Editor is specially designed for competitive programming. It helps you focus on your algorithms and automates compilation, execution and testing of your code. It even fetches test cases for you from different platforms and submits solutions to Codeforces!
CSAcademy online IDE
CSAcademy online IDE has all the features of an ideal IDE, along with a workspace which helps you to work on several files simultaneously and share your code online, easily. Very useful especially when you're trying to get someone else to look into your code.
Difference Checkers
Stress testing is a great way to find out a bug in an algorithm. Stress tests mean to generate a large set of random test cases and then, to check if the efficient algorithm and the brute force algorithm produce the same output. The tools that can be used for this are CSAcademy Diffing Tool and Diffchecker.com
Algorithms Visualisation
VisuAlgo
VisuAlgo is a website perfect for people trying to get an intuitive feel for algorithms. It features animations for the most common data structures and algorithms.
Algorithm Visualizer
Algorithm Visualizer is another website to visualize algorithms, data strucutres and the operations we can do on those data structures. This contains visualisation of almost all the algorithms and data structures, that are generally used.
Recursion Visualizer for any recursion written in JavaScript
Recursion is a website where you can write a recursive code and see the recursion tree come alive. Make sure to try it out, especially to better understand dp and backtracking problems.