Good morning! 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?

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def first_non_repeat(s):

    # fill this in

​

    return ""

​

​

import unittest

​

​

class Test(unittest.TestCase):

    def test_1(self):

        assert first_non_repeat("") == ""

        print("PASSED: first_non_repeat('') should return ''")

​

    def test_2(self):

        assert first_non_repeat("a") == "a"

        print("PASSED: first_non_repeat('a') should return 'a'")

​

    def test_3(self):

        assert first_non_repeat("oh my god dude where is my car") == "g"

        print(

            "PASSED: first_non_repeat('oh my god dude where is my car') should return 'g'"

        )

​

    def test_4(self):

        assert first_non_repeat("asdfsdafdasfjdfsafnnunlfdffvxcvsfansd") == "j"

        print(

            "PASSED: first_non_repeat('asdfsdafdasfjdfsafnnunlfdffvxcvsfansd') should return 'j'"

        )

Here's our guided, illustrated walk-through.

How do I use this guide?