TopCoder, ICPC and IOI all run your code on their machines, and are limited to a small set of languages (C, C++ and Pascal for IOI; C, C++ and Java for ICPC). Others like FB Hacker Cup and Google Code Jam supply the test data, and you just submit the output file; these allow any language.
There is one site (http://spoj.pl) that takes the former approach but supports a huge variety of languages from assembler to Haskell.
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TopCoder, ICPC and IOI all run your code on their machines, and are limited to a small set of languages (C, C++ and Pascal for IOI; C, C++ and Java for ICPC). Others like FB Hacker Cup and Google Code Jam supply the test data, and you just submit the output file; these allow any language.
There is one site (http://spoj.pl) that takes the former approach but supports a huge variety of languages from assembler to Haskell.