27 - First non-repeating character

Don’t say so much, just coding…

Instruction

Write a function named first_non_repeating_letter that takes a string input, and returns the first character that is not repeated anywhere in the string.

For example, if given the input 'stress', the function should return 't', since the letter t only occurs once in the string, and occurs first in the string.

As an added challenge, upper- and lowercase letters are considered the same character, but the function should return the correct case for the initial letter. For example, the input 'sTreSS' should return 'T'.

If a string contains all repeating characters, it should return an empty string ("") or None – see sample tests.

Ruby

Init

def tongues(code)
  #your code here
end

Sample Testing

Test.describe('Simple Tests') do
   it('should handle simple tests') do
     Test.assert_equals(first_non_repeating_letter('a'), 'a')
     Test.assert_equals(first_non_repeating_letter('stress'), 't')
     Test.assert_equals(first_non_repeating_letter('moonmen'), 'e')
   end
   it('should handle empty strings') do
     Test.assert_equals(first_non_repeating_letter(''), '')
   end
 end

Javascript

Init

function firstNonRepeatingLetter(s) {
  // Add your code here
}

Sample Testing

Test.describe('Simple Tests', function() {
  it('should handle simple tests', function() {
    Test.assertEquals(firstNonRepeatingLetter('a'), 'a');
    Test.assertEquals(firstNonRepeatingLetter('stress'), 't');
    Test.assertEquals(firstNonRepeatingLetter('moonmen'), 'e');
  });
});

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Thinking

圖片來源：Unsplash Nikita Kachanovsky

Hint & Reference

• Ruby
  • Ruby - apidock chars
• JavaScript
  • JS - MDN RegExp

Solution

Ruby

# Solution 1
def first_non_repeating_letter(s)
  letter = s.chars.find{ |char| s.chars.map(&:downcase).count(char.downcase) == 1 }
  letter.nil? ? '' : letter
end

# Solution 2
def first_non_repeating_letter(s)
  s.chars.find{ |i| s.downcase.count(i) == 1 || s.upcase.count(i) == 1 } || ''
end

Javascript

// Solution 1
function firstNonRepeatingLetter(s) {
  for(var i in s) {
    if(s.match(new RegExp(s[i],"gi")).length === 1) {
      return s[i];
    }
  }
  return '';
}