Good evening! Here's our prompt for today.

You're given a string of random alphanumerical characters with a length between 0 and 1000.

Write a method to return the first character in the string that does not repeat itself later on.

So if we had a string input of "asdfsdafdasfjdfsafnnunl'", we can see there are multiple letters that are repeated.

Executing firstNonRepeat('asdfsdafdasfjdfsafnnunl') should return 'j' since it's the first letter where there is no duplicate.

Constraints

• The given string can be empty
• The string will only contain lowercase/uppercase alphabets and numerals
• Expected time complexity : O(n)
• Expected space complexity : O(A) where A is the number of ASCII characters

Try to solve this here or in Interactive Mode.

How do I practice this challenge?

xxxxxxxxxx

      "`firstNonRepeat('asdfsdafdasfjdfsafnnunlfdffvxcvsfansd')` should return `'j'`"

var assert = require('assert');

​

function firstNonRepeat(str) {

  // fill this in

  return str;

}

​

try {

  assert.equal(firstNonRepeat(''), '');

​

  console.log('PASSED: ' + "`firstNonRepeat('')` should return `''`");

} catch (err) {

  console.log(err);

}

​

try {

  assert.equal(firstNonRepeat('a'), 'a');

​

  console.log('PASSED: ' + "`firstNonRepeat('a')` should return `'a'`");

} catch (err) {

  console.log(err);

}

​

try {

  assert.equal(firstNonRepeat('oh my god dude where is my car'), 'g');

​

  console.log(

    'PASSED: ' +

      "`firstNonRepeat('oh my god dude where is my car')` should return `'g'`"

We'll now take you through what you need to know.

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