CODEWITHSUNDEEP
javascriptstringalgorithmsubstringindexof
ey dee ey em
ey dee ey em

Reputation: 8593

Where should I find how the indexOf function is written for JavaScript core looks like?

I want to see it because there is an algorithm interview question asked similar thing but no one was able to resolve it without some sort of internal function like indexOf() which would have been perfectly fine except that the requirement was NOT to use an internal function to resolve this. Since I think the best implementation is already there, why don't I just learn from the best? Which I suppose is how they wrote .indexOf() for String already in JavaScript.

My solution was humiliating to even show it... so I decide not to, in other words, there are way too much conditional toggling than I would want to put in there.

Thanks

Question is following

Avoid using built-in functions to solve this challenge. Implement them yourself, since this is what you would be asked to do during a real interview.

Implement a function that takes two strings, s and x, as arguments and finds the first occurrence of the string x in s. The function should return an integer indicating the index in s of the first occurrence of x. If there are no occurrences of x in s, return -1.

Example

For s = "CodefightsIsAwesome" and x = "IA", the output should be strstr(s, x) = -1; For s = "CodefightsIsAwesome" and x = "IsA", the output should be strstr(s, x) = 10. Input/Output

[time limit] 4000ms (js) [input] string s

A string containing only uppercase or lowercase English letters.

Guaranteed constraints: 1 ≤ s.length ≤ 106.

[input] string x

String, containing only uppercase or lowercase English letters.

Guaranteed constraints: 1 ≤ x.length ≤ 106.

[output] integer

An integer indicating the index of the first occurrence of the string x in s, or -1 if s does not contain x

Bitw its from codefight https://codefights.com/interview-practice/task/C8Jdyk3ybixqQdAvM

For anyone interested to test their code in full with all test cases, its here (see where my cursor is pointing to in the image vvv?)

https://codefights.com/interview-practice/topics/strings enter image description here

Upvotes: 3

Views: 2909

Answers (2)

Keith
Keith

Reputation: 24181

no one was able to resolve it

I'm a little shocked that was the case, as it's just 2 simple nested for loops. Eg, it took me less than a few minutes to knock this up.

function strstr(a,b) {
  for (var o = 0; a[o]; o ++)
  {
    var found = true;
    for (var i = 0; b[i]; i ++) {
      if (a[o + i] !== b[i]) { found=false; break; }
    } 
    if (found) return o;
  }
  return -1;
}

var s = "CodefightsIsAwesome";
var x = "IA";

console.log(strstr(s, x));

s = "CodefightsIsAwesome";
x = "IsA";

console.log(strstr(s, x));

Upvotes: 6

Akaino
Akaino

Reputation: 1025

JavaScript runs on ECMAScript Engines. ECMAScript is nothing but the specification of JavaScript. Different browser provides different implementation for that, like Chrome has V8 engine implementation for ECMAScript, similarly Carakan for Opera. Source

So with that in mind... Here you might get some more information on how things work:

ECMA Specification

General MDN entry: Click

Upvotes: 1

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