w3resource

JavaScript: Find longest substring in a given a string without repeating characters

JavaScript Function: Exercise-26 with Solution

Write a JavaScript function to find longest substring in a given a string without repeating characters.

Sample Solution: -

HTML Code:

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <title>Find longest substring in a given a string without repeating characters</title>
</head>
<body>

</body>
</html>

JavaScript Code:

function longest_substring_without_repeating_characters(input) {
var chars = input.split('');
var curr_char;
var str = "";
var longest_string = "";
var hash = {};
for (var i = 0; i < chars.length; i++) {
curr_char = chars[i];
if (!hash[chars[i]]) 
{ 
str += curr_char; 
hash[chars[i]] = {index:i};
}
else 
{
if(longest_string.length <= str.length)
{
longest_string = str;
}
var prev_dupeIndex = hash[curr_char].index;
var str_FromPrevDupe = input.substring(prev_dupeIndex + 1, i);
str = str_FromPrevDupe + curr_char;
hash = {};
for (var j = prev_dupeIndex + 1; j <= i; j++) {
hash[input.charAt(j)] = {index:j};
}
}
}
return longest_string.length > str.length ? longest_string : str;
}
console.log(longest_substring_without_repeating_characters("google.com")); 

console.log(longest_substring_without_repeating_characters("example.com"));

Output:

gle.com
xample.co

Flowchart:

Flowchart: JavaScript function: Longest substring in a given a string without repeating characters

Live Demo:

See the Pen JavaScript - Find longest substring in a given a string without repeating characters-function-ex- 26 by w3resource (@w3resource) on CodePen.


Improve this sample solution and post your code through Disqus

Previous: Write a JavaScript function that accept a list of country names as input and returns the longest country name as output
Next: Write a JavaScript function that returns the longest palindrome in a given string.

What is the difficulty level of this exercise?



JavaScript: Tips of the Day

JavaScript: Implicit type coercion

function sum(a, b) {
  return a + b;
}

sum(1, '2');

JavaScript is a dynamically typed language: we don't specify what types certain variables are. Values can automatically be converted into another type without you knowing, which is called implicit type coercion. Coercion is converting from one type into another.

In this example, JavaScript converts the number 1 into a string, in order for the function to make sense and return a value. During the addition of a numeric type (1) and a string type ('2'), the number is treated as a string. We can concatenate strings like "Hello" + "World", so what's happening here is "1" + "2" which returns "12".

Ref: https://bit.ly/323Y0P6