Add a recursive version of the Longest Common Substring.

Author: trekhleb

src/algorithms/string/longest-common-substring/__test__/longestCommonSubstring.test.js

@@ -7,6 +7,8 @@ describe('longestCommonSubstring', () =>{
 expect(longestCommonSubstring('','ABC')).toBe('');
 expect(longestCommonSubstring('ABABC','BABCA')).toBe('BABC');
 expect(longestCommonSubstring('BABCA','ABCBA')).toBe('ABC');
+expect(longestCommonSubstring('sea','eat')).toBe('ea');
+expect(longestCommonSubstring('algorithms','rithm')).toBe('rithm');
 expect(longestCommonSubstring(
 'Algorithms and data structures implemented in JavaScript',
 'Here you may find Algorithms and data structures that are implemented in JavaScript',

src/algorithms/string/longest-common-substring/__test__/longestCommonSubstringRecursive.test.js

@@ -0,0 +1,17 @@
+importlongestCommonSubstringfrom'../longestCommonSubstringRecursive';
+
+describe('longestCommonSubstringRecursive',()=>{
+it('should find longest common substring between two strings',()=>{
+expect(longestCommonSubstring('','')).toBe('');
+expect(longestCommonSubstring('ABC','')).toBe('');
+expect(longestCommonSubstring('','ABC')).toBe('');
+expect(longestCommonSubstring('ABABC','BABCA')).toBe('BABC');
+expect(longestCommonSubstring('BABCA','ABCBA')).toBe('ABCA');
+expect(longestCommonSubstring('sea','eat')).toBe('ea');
+expect(longestCommonSubstring('algorithms','rithm')).toBe('rithm');
+expect(longestCommonSubstring(
+'Algorithms and data structures implemented in JavaScript',
+'Here you may find Algorithms and data structures that are implemented in JavaScript',
+)).toBe('Algorithms and data structures implemented in JavaScript');
+});
+});

src/algorithms/string/longest-common-substring/longestCommonSubstring.js

@@ -1,4 +1,6 @@
 /**
+ * Longest Common Substring (LCS) (Dynamic Programming Approach).
+ *
  * @param{string} string1
  * @param{string} string2
  * @return{string}

src/algorithms/string/longest-common-substring/longestCommonSubstringRecursive.js

@@ -0,0 +1,36 @@
+/* eslint-disable no-param-reassign */
+/**
+ * Longest Common Substring (LCS) (Recursive Approach).
+ *
+ * @param{string} string1
+ * @param{string} string2
+ * @return{number}
+ */
+exportdefaultfunctionlongestCommonSubstringRecursive(string1,string2){
+/**
+ *
+ * @param{string} s1
+ * @param{string} s2
+ * @return{string} - returns the LCS (Longest Common Substring)
+ */
+constlcs=(s1,s2,memo={})=>{
+if(!s1||!s2)return'';
+
+if(memo[`${s1}:${s2}`])returnmemo[`${s1}:${s2}`];
+
+if(s1[0]===s2[0]){
+returns1[0]+lcs(s1.substring(1),s2.substring(1),memo);
+}
+
+constnextLcs1=lcs(s1.substring(1),s2,memo);
+constnextLcs2=lcs(s1,s2.substring(1),memo);
+
+constnextLongest=nextLcs1.length>=nextLcs2.length ? nextLcs1 : nextLcs2;
+
+memo[`${s1}:${s2}`]=nextLongest;
+
+returnnextLongest;
+};
+
+returnlcs(string1,string2);
+}