Rabin Karp Search Algorithm (TheAlgorithms#1545)

* Search: Rabin-Karp algorithm * Prettier Style * Search: Rabin-Karp adding reference * Search: Rabin-Karp styling and remove unecessary logging * Search: Rabin-Karp review notes * Simplify return * Updated Documentation in README.md --------- Co-authored-by: Lars Müller <[email protected]> Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>

Author: 3 people

DIRECTORY.md

@@ -311,6 +311,7 @@
 *[LinearSearch](Search/LinearSearch.js)
 *[Minesweeper](Search/Minesweeper.js)
 *[QuickSelectSearch](Search/QuickSelectSearch.js)
+*[RabinKarp](Search/RabinKarp.js)
 *[SlidingWindow](Search/SlidingWindow.js)
 *[StringSearch](Search/StringSearch.js)
 *[TernarySearch](Search/TernarySearch.js)

Search/RabinKarp.js

@@ -0,0 +1,64 @@
+/*
+ * Implements the Rabin-Karp algorithm for pattern searching.
+ *
+ * The Rabin-Karp algorithm is a string searching algorithm that uses hashing to find patterns in strings.
+ * It is faster than naive string matching algorithms because it avoids comparing every character in the text.
+ *
+ * This implementation uses a rolling hash function to efficiently compute the hash values of substrings.
+ * It also uses a modulo operator to reduce the size of the hash values, which helps to prevent hash collisions.
+ *
+ * The algorithm returns an array of indices where the pattern is found in the text. If the pattern is not
+ * found, the algorithm returns an empty array.
+ *
+ * [Reference](https://en.wikipedia.org/wiki/Rabin%E2%80%93Karp_algorithm)
+ */
+
+constBASE=256// The number of characters in the alphabet
+constMOD=997// A prime number used for the hash function
+
+functionrabinKarpSearch(text,pattern){
+constpatternLength=pattern.length
+consttextLength=text.length
+consthashPattern=hash(pattern,patternLength)
+consthashText=[]
+constindices=[]
+
+// Calculate the hash of the first substring in the text
+hashText[0]=hash(text,patternLength)
+
+// Precompute BASE^(patternLength-1) % MOD
+constbasePow=Math.pow(BASE,patternLength-1)%MOD
+
+for(leti=1;i<=textLength-patternLength+1;i++){
+// Update the rolling hash by removing the first character
+// and adding the next character in the text
+hashText[i]=
+(BASE*(hashText[i-1]-text.charCodeAt(i-1)*basePow)+
+text.charCodeAt(i+patternLength-1))%
+MOD
+
+// In case of hash collision, check character by character
+if(hashText[i]<0){
+hashText[i]+=MOD
+}
+
+// Check if the hashes match and perform a character-wise comparison
+if(hashText[i]===hashPattern){
+if(text.substring(i,i+patternLength)===pattern){
+indices.push(i)// Store the index where the pattern is found
+}
+}
+}
+
+returnindices
+}
+
+functionhash(str,length){
+lethashValue=0
+for(leti=0;i<length;i++){
+hashValue=(hashValue*BASE+str.charCodeAt(i))%MOD
+}
+returnhashValue
+}
+
+export{rabinKarpSearch}

Search/test/RabinKarp.test.js

@@ -0,0 +1,30 @@
+import{rabinKarpSearch}from'../RabinKarp'
+
+describe('Rabin-Karp Search',function(){
+it('should find the pattern in the text',function(){
+consttext='ABABDABACDABABCABAB'
+constpattern='DAB'
+constexpected=[4,9]
+
+constresult=rabinKarpSearch(text,pattern)
+expect(result).to.deep.equal(expected)
+})
+
+it('should handle multiple occurrences of the pattern',function(){
+consttext='ABABABABABAB'
+constpattern='ABAB'
+constexpected=[2,4,6,8]
+
+constresult=rabinKarpSearch(text,pattern)
+expect(result).to.deep.equal(expected)
+})
+
+it('should handle pattern not found',function(){
+consttext='ABCD'
+constpattern='XYZ'
+constexpected=[]
+
+constresult=rabinKarpSearch(text,pattern)
+expect(result).to.deep.equal(expected)
+})
+})