title: Find if all letters in a string are unique
body: <p>I need to know if all letters in a string are unique. For a string to be unique, a letter can only appear once. If all letters in a string are distinct, the string is unique. If one letter appears multiple times, the string is not unique.</p>
  
  <pre><code>"Cwm fjord veg balks nth pyx quiz."
  # =&gt; All 26 letters are used only once. This is unique
  
  "This is a string"
  # =&gt; Not unique, i and s are used more than once
  
  "two"
  # =&gt; unique, each letter is shown only once
  </code></pre>
  
  <p>I tried writing a function that determines whether or not a string is unique.</p>
  
  <pre><code>def unique_characters(string)
    for i in ('a'..'z')
    if string.count(i) &gt; 1
      puts "This string is unique"
    else
      puts "This string is not unique"
    end
  end
  
  unique_characters("String")
  </code></pre>
  
  <p>I receive the output</p>
  
  <pre><code>"This string is unique" 26 times.
  </code></pre>
  
  <p>Edit:</p>
  
  <p>I would like to humbly apologize for including an incorrect example in my OP. I did some research, trying to find pangrams, and assumed that they would only contain 26 letters. I would also like to thank you guys for pointing out my error. After that, I went on wikipedia to find a perfect pangram (I wrongly thought the others were perfect).</p>
  
  <p>Here is the link for reference purposes</p>
  
  <p><a href="http://en.wikipedia.org/wiki/List_of_pangrams#Perfect_pangrams_in_English_.2826_letters.29" rel="nofollow">http://en.wikipedia.org/wiki/List_of_pangrams#Perfect_pangrams_in_English_.2826_letters.29</a></p>
  
  <p>Once again, my apologies.</p>