TinyURL的风格独特的code：潜在的算法，prevent碰撞 [英] Tinyurl-style unique code: potential algorithm to prevent collisions

问题描述

我有一个系统，需要一个唯一的6位code重新present一个对象，我试图想一个好的算法生成他们。下面是pre-请求数：

I have a system that requires a unique 6-digit code to represent an object, and I'm trying to think of a good algorithm for generating them. Here are the pre-reqs:

• 在我使用的一个基地 - 20系统（没有上限，数字，元音，或l至prevent混乱和下流话）
  • 基-20可允许64万种组合
  • I'm using a base-20 system (no caps, numbers, vowels, or l to prevent confusion and naughty words)
    • The base-20 allows 64 million combinations

    我听起来像它会工作的想法，但我不是在数学不够好，弄清楚如何实现它：如果我从0开始，增量N，则转换为基础-20，似乎就像应该有N个部分的价值，让我重复之前的任何指望从0-63,999,999每个值。

    I had an idea that sounded like it would work, but I'm not good enough at math to figure out how to implement it: if I start at 0 and increment by N, then convert to base-20, it seems like there should be some value for N that lets me count each value from 0-63,999,999 before repeating any.

    例如，从0到9的使用，N = 3（10如此模3）去：0，3，6，9，2,5，8,1，4，7

    For example, going from 0 through 9 using N=3 (so 10 mod 3): 0, 3, 6, 9, 2, 5, 8, 1, 4, 7.

    有一些神奇的数学方法计算出的N值一些较大的数字，能够在整个范围内来算不重复？理想情况下，我选择了一些排序将围绕一套这样的，这是不是很明显，有一个图案跳跃的，但我不知道如何可能是。

    Is there some magic math method for figuring out values of N for some larger number that is able to count through the whole range without repeating? Ideally, the number I choose would sort of jump around the set such that it wasn't obvious that there was a pattern, but I'm not sure how possible that is.

    另外，散列算法，保证值0-64万美元将工作的独特性，但我的方式太愚蠢知道这是可能的。

    Alternatively, a hashing algorithm that guaranteed uniqueness for values 0-64 million would work, but I'm way too dumb to know if that's possible.

    推荐答案

    所有你需要的是一个数字，没有共享的因素与你的密钥空间。最简单数值是使用一个质数。你可以谷歌的大素数，或使用<一个href="http://primes.utm.edu/lists/small/10000.txt">http://primes.utm.edu/lists/small/10000.txt

    All you need is a number that shares no factors with your key space. Easiest value is to use a prime number. You can google for large primes, or use http://primes.utm.edu/lists/small/10000.txt

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