Google Code Jam

About - Code Jam
"Google’s longest running global coding competition, Code Jam, calls on programmers around the world to solve challenging, algorithmic puzzles against the clock. "

Past Contests | Google Code Jam

"results and code from past rounds of Code Jam (from 2008 to 2017) and related spin-offs... you can try the problems yourself"

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About - Project Euler

"Project Euler is a series of challenging mathematical/computer programming problems that will require more than just mathematical insights to solve. Although mathematics will help you arrive at elegant and efficient methods, the use of a computer and programming skills will be required to solve most problems."

LeetCode - The World's Leading Online Programming Learning Platform

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