Find common substring of > 1 character length between two strings in JS
As per title, I need to find the common substring between two strings, which is longer than 1 character (so one that’s one character long doesn’t count).
I am trying to firstly compare two strings and if their characters match, to return true. Else, to return false. So far I have this code:
function SubstringTest(str1, str2){ for ( let i = 0; i < str1.length; i++) { for (let j = 0; j < str2.length; j++) { if ((str1[i]) === (str2[j])) { return true } else { return false } } } } SubstringTest("something", "home") but I can’t understand why it doesn’t work. Can anybody point me in the right direction? Thanks.
This is the bruteforce, non-optimal solution:
let commonSubstring = (str1, str2, minLen=1) => { let best = { len: 0, off1: null, off2: null }; for (let off1 = 0; off1 < str1.length - minLen; off1++) { for (let off2 = 0; off2 < str2.length - minLen; off2++) { // Holds the number of characters that match let maxLen = Math.min(str1.length - off1, str2.length - off2); let len = 0; while (len < maxLen && str1[off1 + len] === str2[off2 + len]) len++; // Store this result if it's the best yet if (len > best.len) best = { len, off1, off2 }; } } // We can now assert that str1.slice(best.off1, best.len) === str2.slice(best.off2, best.len) return best.len >= minLen ? str1.slice(best.off1, best.off1 + best.len) : null; }; let tests = [ [ 'mustard', 'hustler' ], [ 'lemon', 'harlem' ], [ 'marshmallow', 'hollow' ], [ 'marshmallow', 'marshal' ], [ 'jefferson', 'jeffery' ] ]; console.log('Examples:'); for (let [ str1, str2 ] of tests) { console.log(`Strings "${str1}" and "${str2}" share substring "${commonSubstring(str1, str2, 2)}"`); }The idea is to iterate all pairings of offsets within str1 and str2. Eventually we’ll arrive at the offsets where the longest sequence of shared characters occurs.
Note that I provided minLen as a parameter. You can set it to 2 if you want to discard any results less than 2 characters long.
function SubstringTest(str1, str2){ var matchingText = ""; for ( let i = 0; i < str1.length; i++) { if(str1[i] == str2[i]){ matchingText+= str1[i]; } } if(matchingText.length > 0) return true; return false; } 
