# 99 Haskell Problems

## Problem 15

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

Example:

* (repli '(a b c) 3) (A A A B B B C C C)

Example in Haskell:

> repli "abc" 3 "aaabbbccc"

Solution:

repli :: [a] -> Int -> [a] repli [] _ = [] repli x 1 = x repli (x:xs) n = (repli1 x n) ++ (repli xs n) repli1 :: a -> Int -> [a] repli1 x 0 = [] repli1 x n = [x] ++ (repli1 x (n-1))

A simpler way is to use the function replicate and concatMap as shown in the solution.

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

The function replicate takes an Int, n and an element, x and duplicate the element n times. By giving replicate function only an argument n, we created a new function that takes an element x and duplicate it n time. We can compare the type of replicate and (replicate 2) to see the different.

> :t replicate replicate :: Int -> a -> [a] > :t (replicate 2) (replicate 2) :: a -> [a]