Add Hamming.

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Oleksii Trekhleb 2018-04-24 14:45:55 +03:00
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commit 66ebd7859a
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* [FisherYates Shuffle](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/math/fisher-yates) - random permutation of a finite sequence
* **String**
* [Levenshtein Distance](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/string/levenshtein-distance) - minimum edit distance between two sequences
* Hamming
* [Hamming Distance](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/string/hamming-distance) - number of positions at which the symbols are different
* Huffman
* Knuth Morris Pratt
* Longest common subsequence

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# Hamming Distance
the Hamming distance between two strings of equal length is the
number of positions at which the corresponding symbols are
different. In other words, it measures the minimum number of
substitutions required to change one string into the other, or
the minimum number of errors that could have transformed one
string into the other. In a more general context, the Hamming
distance is one of several string metrics for measuring the
edit distance between two sequences.
## Examples
The Hamming distance between:
- "ka**rol**in" and "ka**thr**in" is **3**.
- "k**a**r**ol**in" and "k**e**r**st**in" is **3**.
- 10**1**1**1**01 and 10**0**1**0**01 is **2**.
- 2**17**3**8**96 and 2**23**3**7**96 is **3**.
## References
[Wikipedia](https://en.wikipedia.org/wiki/Hamming_distance)

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import hammingDistance from '../hammingDistance';
describe('hammingDistance', () => {
it('should throw an error when trying to compare the strings of different lengths', () => {
const compareStringsOfDifferentLength = () => {
hammingDistance('a', 'aa');
};
expect(compareStringsOfDifferentLength).toThrowError();
});
it('should calculate difference between two strings', () => {
expect(hammingDistance('a', 'a')).toBe(0);
expect(hammingDistance('a', 'b')).toBe(1);
expect(hammingDistance('abc', 'add')).toBe(2);
expect(hammingDistance('karolin', 'kathrin')).toBe(3);
expect(hammingDistance('karolin', 'kerstin')).toBe(3);
expect(hammingDistance('1011101', '1001001')).toBe(2);
expect(hammingDistance('2173896', '2233796')).toBe(3);
});
});

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/**
* @param {string} a
* @param {string} b
* @return {number}
*/
export default function hammingDistance(a, b) {
if (a.length !== b.length) {
throw new Error('Strings must be of the same length');
}
let distance = 0;
for (let i = 0; i < a.length; i += 1) {
if (a[i] !== b[i]) {
distance += 1;
}
}
return distance;
}