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Added Levenshtein distance (a.k.a edit distance) algorithm to strings… #427

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Merged
ruppysuppy merged 1 commit into from
Oct 10, 2020
Merged

Added Levenshtein distance (a.k.a edit distance) algorithm to strings… #427

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51 changes: 51 additions & 0 deletions String/LevenshteinDistance.js
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Original file line number Diff line number Diff line change
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/* The Levenshtein distance (a.k.a edit distance) is a
measure of similarity between two strings. It is
defined as the minimum number of changes required to
convert string a into string b (this is done by
inserting, deleting or replacing a character in
string a).
The smaller the Levenshtein distance,
the more similar the strings are. This is a very
common problem in the application of Dynamic Programming.
*/

const levenshteinDistance = (a, b) => {
// Declaring array 'D' with rows = len(a) + 1 and columns = len(b) + 1:
const distanceMatrix = Array(b.length + 1)
.fill(null)
.map(() => Array(a.length + 1).fill(null))

// Initialising first column:
for (let i = 0; i <= a.length; i += 1) {
distanceMatrix[0][i] = i
}

// Initialising first row:
for (let j = 0; j <= b.length; j += 1) {
distanceMatrix[j][0] = j
}

for (let j = 1; j <= b.length; j += 1) {
for (let i = 1; i <= a.length; i += 1) {
const indicator = a[i - 1] === b[j - 1] ? 0 : 1
// choosing the minimum of all three, vis-a-vis:
distanceMatrix[j][i] = Math.min(
distanceMatrix[j][i - 1] + 1, // deletion
distanceMatrix[j - 1][i] + 1, // insertion
distanceMatrix[j - 1][i - 1] + indicator // substitution
)
}
}

console.log(
'Levenshtein Distance between ' +
a +
' and ' +
b +
' is = ' +
distanceMatrix[b.length][a.length]
)
return distanceMatrix[b.length][a.length]
}

export { levenshteinDistance }
26 changes: 26 additions & 0 deletions String/LevenshteinDistance.test.js
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import levenshteinDistance from './LevenshteinDistance'

describe('levenshteinDistance', () => {
it('should calculate edit distance between two strings', () => {
expect(levenshteinDistance('', '')).toBe(0)
expect(levenshteinDistance('a', '')).toBe(1)
expect(levenshteinDistance('', 'a')).toBe(1)
expect(levenshteinDistance('abc', '')).toBe(3)
expect(levenshteinDistance('', 'abc')).toBe(3)

// Should just add I to the beginning.
expect(levenshteinDistance('igloo', 'gloo')).toBe(1)

// Should just substitute i with o, m with g and insert e at end
expect(levenshteinDistance('firm', 'forge')).toBe(3)

// Should just substitute i with s, g with i, h with t and delete f from front
expect(levenshteinDistance('fighting', 'sitting')).toBe(4)

// Should add 4 letters b, a, s and e at the beginning.
expect(levenshteinDistance('ball', 'baseball')).toBe(4)

// Should delete 4 letters b, a, s and e at the beginning.
expect(levenshteinDistance('baseball', 'foot')).toBe(4)
})
})