What are the most important algorithms? [closed]

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Christoph Koutschan has set up an interesting survey that tries to identify the most important algorithms "in the world". Since one of the criteria is that "the algorithm has to be widely used" I though that extending the survey to the huge group of users at Stack Overflow would be a natural thing to do.

So, what do you think? Which algorithms deserve a place in the Algorithm Hall of Fame?

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I somewhat like this algorithm:

1. Write code.

2. Test code. If buggy, go to step 3. If not, go to step 4.

3. Rewrite code, then go back to step 2.

4. Get somebody else to test your code. If they discover any bugs, return to step 3, otherwise go to step 5.

5. Congratulations, your code has no obvious bugs! Now you wait for a user to stumble upon a hidden one, in which case you return to step 3 once again unless you're lucky and are no longer providing support for the code in question.

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I'd say binary search since it's usually the first algorithm people learn. And the RSA encryption algorithms are pretty important.

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Hashing, since it's the basis for so much in security, data structures, etc. Hashing algorithms have generated a lot of Ph.D. dissertations.