How to check regex true on no repeating letters?

Question

I need to check if a word is Isogram, the meaning of Isogram, is that a word has no repeating letters.

I need to implement a function that determines whether a string that contains only letters is an isogram. Assume the empty string is an isogram. Ignore letter case.

Here is a test case

isIsogram( "Dermatoglyphics" ) == true
isIsogram( "aba" ) == false
isIsogram( "moOse" ) == false // -- ignore letter case

I am thinking on do this with a Regex.

function isIsogram(str){
  //...
}

can you help?

Why do you want to do it using regex? Just use a set of characters. — Oriol, Feb 17 '16 at 22:28
@Oriol I thought it was the proper way. is there a better way ? — Non, Feb 17 '16 at 22:29
@NietzscheProgrammer Can't you just put the characters of the string in an array and call distinct on it? If the length of original array differs from the distinct one it's an isogram. — Alexander Derck, Feb 17 '16 at 22:34
bah lame closure... the question this was marked as a duplicate of has terrible answers... — thedarklord47, Feb 17 '16 at 22:53
I reposted my answer on the linked question here: http://stackoverflow.com/a/35469422/1800023 — thedarklord47, Feb 17 '16 at 22:58

score 12 · Accepted Answer · answered Feb 17 '16 at 22:34

12

as simple as that

function isIsogram (str) {

    return !/(\w).*\1/i.test(str);
}

answered Feb 17 '16 at 22:34

orvi

3,142
1
23
36

For simplicity and smallest code +1 – Err Feb 17 '16 at 22:41
1

this is incorrect as it does not ignore case. remove the `/i` – thedarklord47 Feb 17 '16 at 22:41
plus @Err my code is one char smaller so :p – thedarklord47 Feb 17 '16 at 22:49

thedarklord47 · Answer 2 · 2016-02-17T22:46:05.310

4

This will do:

function isIsogram (str) {
    return !/(.).*\1/.test(str);
}

edited Feb 17 '16 at 22:46

answered Feb 17 '16 at 22:39

thedarklord47

3,183
3
26
55

Sorry for ressurecting and old submission, can you walk through how the syntax is matching the string. The readability is a little confusing – Kode_12 Aug 20 '16 at 20:28
`(.)` capture any letter. `.*` followed by any sequence of letters including nothing. `\1` followed by the first letter we captured. In other words, this will match any string that has at least two of the same letters. Take the opposite of that boolean. – thedarklord47 Aug 22 '16 at 18:44

score 2 · Answer 3 · answered Feb 17 '16 at 22:35

You can use it like this by converting the input to a lower case:

var re = /^(?:([a-z])(?!.*\1))*$/;

function isIsogram(str) {
   return re.test( str.toLowerCase() );
}

Testing:

isIsogram("Dermatoglyphics")
true
re.test("aba")
false
isIsogram("moOse")
false

How to check regex true on no repeating letters?

3 Answers3