> For the complete documentation index, see [llms.txt](https://trizen.gitbook.io/sidef-lang/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://trizen.gitbook.io/sidef-lang/programming_tasks/l/longest_common_substring.md).

# Longest common substring

```ruby
func createSubstrings(String word) -> Array {
  gather {
    combinations(word.len+1, 2, {|i,j|
        take(word.substr(i, j-i))
    })
  }
}

func findLongestCommon(String first, String second) -> String {
    createSubstrings(first) & createSubstrings(second) -> max_by { .len }
}

say findLongestCommon("thisisatest", "testing123testing")
```

## Output:

```
test
```