Longest Common Prefix in Javascript

Question

I am trying to solve the Leet Code challenge 14. Longest Common Prefix:

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 "".

Example 1:

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

Example 2:

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

Explanation: There is no common prefix among the input strings.

Constraints:

• 1 <= strs.length <= 200
• 0 <= strs[i].length <= 200
• strs[i] consists of only lower-case English letters.

My solution:

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

var longestCommonPrefix = function (strs) {
  for (let i = 0; i < strs.length; i++) {
    for (let j = 0; j < strs[i].length; j++) {
       // console.log(strs[i+2][j]);
      if (strs[i][j] == strs[i + 1][j] && strs[i + 1][j] ==strs[i + 2][j]) {
        return (strs[i][j]);
        
      } else {
        return "0";
      }
    }
  }
};

console.log(longestCommonPrefix(strs));

Output: f

How can I iterate over every character and check if it is same and then go for next and if it fails then the longest common prefix will be returned?

Answer 1

As the longest common prefix must occur in every string of the array you can jus iterate over the length and check if all words have the same char at that index until you find a difference

function prefix(words){
  // check border cases size 1 array and empty first word)
  if (!words[0] || words.length ==  1) return words[0] || "";
  let i = 0;
  // while all words have the same character at position i, increment i
  while(words[0][i] && words.every(w => w[i] === words[0][i]))
    i++;
  
  // prefix is the substring from the beginning to the last successfully checked i
  return words[0].substr(0, i);
}

console.log(1, prefix([]));
console.log(2, prefix([""]));
console.log(3, prefix(["abc"]));
console.log(4, prefix(["abcdefgh", "abcde", "abe"]));
console.log(5, prefix(["abc", "abc", "abc"]));
console.log(6, prefix(["abc", "abcde", "xyz"]));