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No need to do a pre-pass just to compute the length: Two minor details: In C, you should add void to the parameter list of functions that take no arguments, so main should be int main(void). String hash function #2. What is the difference between non-type template parameters in C++17 and C++11? For every substring length $l$ we construct an array of hashes of all substrings of length $l$ multiplied by the same power of $p$. Hash function for strings. Hashes the string between S1 and S2. Perhaps even some string hash functions are better suited for German, than for English or French words. Popular hash functions generate values between 160 and 512 bits. We wrote a paper about it: Strongly universal string hashing is fast. It is common to want to use string-valued keys in hash tables; What is a good hash function for strings? I think the function ht_hash has some severe flaws. Hash code is the result of the hash function and is used as the value of the index for storing a key. The functional call returns a hash value of its argument: A hash value is a value that depends solely on its argument, returning always the same value for the same argument (for a given execution of a program). set of directories numbered 0..SOME NUMBER and find the image files by hashing a normalized string that represented a filename. This is a large number, but still small enough so that we can perform multiplication of two values using 64-bit integers. Returns the hash function object used by the unordered_map container. CS 2505 Computer Organization I C07: Hash Table in C Version 2.00 This is a purely individual assignment! hash.c hash function for strings in C scramble by using 117 instead of 256 Uniform hashing: use a different random multiplier for each digit. Implementation in C Here is an example of calculating the hash of a string $s$, which contains only lowercase letters. What if we compared a string $s$ with $10^6$ different strings. The General Hash Function Algorithm library contains implementations for a series of commonly used additive and rotative string hashing algorithm in the Object Pascal, C and C++ programming languages I don't see a need for reinventing the wheel here. From the obvious algorithm involving sorting the strings, we would get a time complexity of $O(n m \log n)$ where the sorting requires $O(n \log n)$ comparisons and each comparison take $O(m)$ time. It is easy to generate and compare hash values using the cryptographic resources contained in the System.Security.Cryptography namespace. The reason why the opposite direction doesn't have to hold, if because there are exponential many strings. The goal of it is to convert a string into an integer, the so-called hash of the string. Different strings can return the same hash code. We calculate the hash for each string, sort the hashes together with the indices, and then group the indices by identical hashes. 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