Longest string with two distinct characters in JavaScript

We are required to write a JavaScript function that takes in a string as the first argument and a number (smaller than the length of string) as the second argument. The function should delete characters from the original string and prepare a new string such that it's the longest string containing at most two distinct characters.

Then at last the function should return the length of that desired string.

For example: If the input string is −

const str = 'kjeljsdl';

Then the output should be −

const output = 4;

because the longest substring with at most 2 distinct characters is 'jljl'

Example

The code for this will be −

 Live Demo

const str = 'kjeljsdl'; const longestSubstring = (str = '') => {    const { length } = str;    if (length <= 1){       return 0;    };    const keys = [...new Set(str)];    const arr = [];    let max = 0;    for (let i = 0; i < keys.length - 1; i++) {       for (let j = i + 1; j < keys.length; j++) {          arr.push(keys[i] + keys[j]);       }    }    arr.forEach(item => {       let sub = '';       for (let i = 0; i < str.length; i++) {          if (sub[sub.length - 1] === str[i]) {             sub = '';             break;          }          if (item.includes(str[i])) {             sub += str[i];          }       }       if (sub && sub.length > max){          max = sub.length;       };    });    return max; } console.log(longestSubstring(str));

Output

And the output in the console will be −

4