# 99 questions/Solutions/15

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< 99 questions | Solutions

Revision as of 09:42, 23 January 2012 by Redshift (talk | contribs) (discovered an interesting solution that was not on here)

(**) Replicate the elements of a list a given number of times.

```
repli :: [a] -> Int -> [a]
repli xs n = concatMap (replicate n) xs
```

or, in Pointfree style:

```
repli = flip $ concatMap . replicate
```

alternatively, without using the `replicate`

function:

```
repli :: [a] -> Int -> [a]
repli xs n = concatMap (take n . repeat) xs
```

or, using the list monad:

```
repli :: [a] -> Int -> [a]
repli xs n = xs >>= replicate n
```

or, a more verbose solution without the use of `replicate`

:

```
repli :: [a] -> Int -> [a]
repli xs n = foldl (\acc e -> acc ++ repli' e n) [] xs
where
repli' _ 0 = []
repli' x n = x : repli' x (n-1)
```

or, a convoluted recursive solution that only uses cons:

```
repli :: [a] -> Int -> [a]
repli [] _ = []
repli (x:xs) n = foldl (\f _ -> (x:) . f) (repli xs) [1..n] n
```