longestSubstring.js

// How do you find the length of the longest substring without repeating
//characters?

const longestSubstring = str => {
  if (typeof str !== "string" || !str.length) {
    return null;
  }

  const letters = str
    .toLowerCase()
    .replace(/[\W_]/g, "")
    .split("");

  let results = [];
  let maxLength = 0;

  for (let i = 0; i < letters.length; i++) {
    if (results.indexOf(letters[i]) === -1) {
      results.push(letters[i]);
    } else {
      i = i - 1;
      results = [];
    }
    if (maxLength < results.length) {
      maxLength = results.length;
    }
  }
  return maxLength;
};

//Time-complexity: O(n)
//Test cases

const caseTest = [
  { input: "", output: null },
  { input: 123, output: null },
  { input: "abBcB", output: 4 },
  { input: "abcdefgh", output: 8 },
  { input: "abccdeggh", output: 4 },
  { input: "abcddghabcdf", output: 6 },
  { input: "abcCdEggh", output: 4 },
  { input: "abccde ggh", output: 4 },
  { input: "abc@cde_ggh", output: 4 },
  { input: "Sh/i. lp@IA", output: 5 }
];
caseTest.forEach(({ input, output }, index) => {
  console.log(
    `caseTest: ${index} (${input}) (${
      longestSubstring(input) === output ? "success" : "failure"
    })`
  );
});

This program is already considering upper case alphabets and lower case alphabets different, it is evident in third test case.