Largest Substring Between Two Equal Characters in a string in JavaScript

We are required to write a JavaScript function that takes in a string of characters as the only argument.

The function should find that longest string which is sandwiched between two identical characters and return its length.

For example −

If the input string is −

const str = 'sadtrsewak';

Then the output should be −

const output = 6;

because between two 'a' we have the longest desired substring of length 6.

Example

Following is the code −

const str = 'sadtrsewak'; const longestSubstringBetween = (str = '') => {    const map = {};    let res = -1;    for(let i = 0; i < str.length; i++){       const el = str[i];       if(map.hasOwnProperty(str[i])){          res = Math.max(res, i - map[el] - 1);       }else{          map[el] = i;       };    };    return res; } console.log(longestSubstringBetween(str));

Output

Following is the console output −

6