Find longest substring without repeating characters

Question

Given a string S of length N find longest substring without repeating characters.

Example:

Input:

Answer 1

Here are two ways to approach this problem in JavaScript.

A Brute Force approach is to loop through the string twice, checking every substring against every other substring and finding the maximum length where the substring is unique. We'll need two functions: one to check if a substring is unique and a second function to perform our double loop.

// O(n) time
const allUnique = str => {
  const set = [...new Set(str)];
  return (set.length == str.length) ? true: false;
}

// O(n^3) time, O(k) size where k is the size of the set
const lengthOfLongestSubstring = str => {
  let result = 0,
      maxResult = 0;
  for (let i=0; i maxResult) {
          maxResult = result;
        }
      }
    }
  return maxResult;
  }
}

This has a time complexity of O(n^3) since we perform a double loop O(n^2) and then another loop on top of that O(n) for our unique function. The space is the size of our set which can be generalized to O(n) or more accurately O(k) where k is the size of the set.

A Greedy Approach is to loop through only once and keep track of the maximum unique substring length as we go. We can use either an array or a hash map, but I think the new .includes() array method is cool, so let's use that.

const lengthOfLongestSubstring = str => {
  let result = [],
      maxResult = 0;

  for (let i=0; i

This has a time complexity of O(n) and a space complexity of O(1).