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Ilya Kantor 2017-03-21 17:14:05 +03:00
parent ab9ab64bd5
commit 97c8f22bbb
289 changed files with 195 additions and 172 deletions
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10-regular-expressions-javascript/11-regexp-alternation/01-find-programming-language/solution.md
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The first idea can be to list the languages with `|` in-between.
But that doesn't work right:
```js run
let reg = /Java|JavaScript|PHP|C|C\+\+/g;
let str = "Java, JavaScript, PHP, C, C++";
alert( str.match(reg) ); // Java,Java,PHP,C,C
```
The regular expression engine looks for alternations one-by-one. That is: first it checks if we have `match:Java`, otherwise -- looks for `match:JavaScript` and so on.
As a result, `match:JavaScript` can never be found, just because `match:Java` is checked first.
The same with `match:C` and `match:C++`.
There are two solutions for that problem:
1. Change the order to check the longer match first: `pattern:JavaScript|Java|C\+\+|C|PHP`.
2. Merge variants with the same start: `pattern:Java(Script)?|C(\+\+)?|PHP`.
In action:
```js run
let reg = /Java(Script)?|C(\+\+)?|PHP/g;
let str = "Java, JavaScript, PHP, C, C++";
alert( str.match(reg) ); // Java,JavaScript,PHP,C,C++
```