Leet Code - Longest Common Prefix

#javascript #beginners #programming #tutorial

Problem Statement

Write a function to find the longest common prefix string amongst an array of strings.
If there is no common prefix, return an empty string "".

Algorithm

if array is empty, return a prefix of empty string Or if
array has 1 word, return the whole word.
Iterate through letter of first word of Array , and compare
those letters to same Indexed letter to other world.

Example

   let strs = ["flower","flow","flight"]
   So What above line meaning is -
   str[0][0] === str[1][0],
   str[0][1] === str[1][1] and so on....

if the letters match continue to next set of letters
otherwise return the prefix
If the letter is no longer matching then the first word
will mark where the longest common prefix is, so
we add to our empty string.

First Try to Solve Problem using Algorithm

Javascript Function for Longest Common Prefix

/**
 * @param {string[]} strs
 * @return {string}
 */
var longestCommonPrefix = function(strs) {
let result = "";
//array is empty, return a prefix of empty string
if (strs.length === 0) {return ""}

//array has 1 word, return the whole word
if (strs.length === 1) {return strs[0]}

//Iterate through letter of first word of Array
for(let i=0 ; i<strs[0].length ; i++){
//compare those letters to same Indexed letter to other world.
 for(let j=1 ; j< strs.length ; j++){
 if(strs[0][i] == strs[j][i]){
     continue;
 }else{
     return result
 }
 }

/*If the letter is no longer matching then the first word 
  will mark where the longest common prefix is, so 
  we add to our empty string*/
result += strs[0][i];
}
return result;    
};

Test Cases

Input: strs = ["flower","flow","flight"] Output: "fl"

Input: strs = ["dog","racecar","car"] Output: ""

Input: strs = ["",""] Output: ""

Top comments (3)

Frank Wisniewski • Jul 27 '22

"use strict";
  var longestCommonPrefix = (strs) =>
    strs.join()
      .match(/^(?<prefix>[\w\p{Emoji}]*)[\w\p{Emoji}]*(?:,\1[\w\p{Emoji}]*)*$/u)
        .groups.prefix

  let strs = ["flower","flow","flight"]

  console.log(
    longestCommonPrefix(strs)
  )