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

JavaScript Function: Exercise-26 with Solution

Longest Substring Without Repeating Characters

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

Sample Solution-1:

JavaScript Code:

// Function to find the longest substring without repeating characters
function longest_substring_without_repeating_characters(input) {
  // Split the input string into an array of characters
  var chars = input.split('');
  var curr_char;
  var str = "";
  var longest_string = "";
  var hash = {};

  // Loop through each character in the input string
  for (var i = 0; i < chars.length; i++) {
    curr_char = chars[i];

    // Check if the character is not already in the hash table
    if (!hash[chars[i]]) { 
      // Add the character to the current substring
      str += curr_char; 
      // Update the hash table with the character and its index
      hash[chars[i]] = {index:i};
    } else {
      // If there's a repeating character, compare lengths and update if necessary
      if (longest_string.length <= str.length) {
        longest_string = str;
      }
      // Get the index of the previous occurrence of the repeating character
      var prev_dupeIndex = hash[curr_char].index;
      // Extract the substring from the previous occurrence to the current index
      var str_FromPrevDupe = input.substring(prev_dupeIndex + 1, i);
      // Update the current substring with the new non-repeating characters
      str = str_FromPrevDupe + curr_char;
      // Reset the hash table for the new substring
      hash = {};
      // Update the hash table with the characters and their indices in the new substring
      for (var j = prev_dupeIndex + 1; j <= i; j++) {
        hash[input.charAt(j)] = {index:j};
      }
    }
  }

  // Return the longest substring (either the current substring or the previously found longest)
  return longest_string.length > str.length ? longest_string : str;
}

// Example usage:
console.log(longest_substring_without_repeating_characters("google.com")); 
console.log(longest_substring_without_repeating_characters("example.com"));  

Output:

gle.com
xample.co

Flowchart:

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.

Sample Solution-2:

JavaScript Code:

// Function to find the longest substring without repeating characters
function longest_substring_without_repeating_characters(input) {
  let longestSubstring = "";
  let start = 0;
  let charIndexMap = {};

  for (let end = 0; end < input.length; end++) {
    let char = input[end];

    if (charIndexMap[char] !== undefined && charIndexMap[char] >= start) {
      // If repeating character found, update start index
      start = charIndexMap[char] + 1;
    }

    // Update the index of the current character
    charIndexMap[char] = end;

    // Update the longest substring
    let currentSubstring = input.slice(start, end + 1);
    if (currentSubstring.length > longestSubstring.length) {
      longestSubstring = currentSubstring;
    }
  }

  return longestSubstring;
}

// Example usage:
console.log(longest_substring_without_repeating_characters("google.com")); 
console.log(longest_substring_without_repeating_characters("example.com"));

Output:

gle.com
xample.co

Flowchart:

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.