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Topcoder : TopCoder is indeed the world’s largest competitive software development community where developers from all over the world take part in.
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CodeChef : CodeChef is a non-commercial organization operated by DirectI, an Indian software company based in Mumbai, India.
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Google Code Jam : Google Code Jam is an annual programming competition sponsored and supported by Google itself.
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Codeforces : Codeforces is an online programming platform where you can practice variety of problems and submit competitive ones and compete on problems submitted by other users.
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ACM-ICPC : ACM – ICPC is one of the world’s largest programming contest conducted annually.
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Leetcode(https://leetcode.com) : LeetCode Online Judge is a platform for preparing technical coding interviews and assessing your knowledge of data structures and algorithms.
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Hihocoder : Learn and Practise, Compete and Make Friends, Stand out and Get hired. register. or login with. Hiho weekly.