What's the idea of doing x mod 1000000007? [closed]

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Closed 7 years ago.

In many programming problems (e.g. some Project Euler problems) we are asked to report the answer as the remainder left after dividing the answer by 1,000,000,007.

Why not any other number?

Edit: 2 years later, here's what I know: the number is a big prime, and any answer to such a question is so large that it makes sense to report a remainder instead (as the number may be too large for a native datatype to handle).

回答1:

Let me play a telepathist. 1000...7 are prime numbers and 1000000007 is the biggest one that fits in 32-bit integer. Since prime numbers are used to calculate hash (by finding the remainder of the division by prime), 1000000007 is good for calculating 32-bit hash.

来源：https://stackoverflow.com/questions/12578376/whats-the-idea-of-doing-x-mod-1000000007