Haskell Program to Print Diamond Star Pattern

In Haskell, to print Diamond star pattern we will be using mapM_, reverse, unlines and replicate functions. In the first example, we are going to use ( diamondStarPattern n = unlines $ topHalf ++ bottomHalf where topHalf = [replicate (n - i) ' ' ++ replicate ((2 * i) - 1) '*' | i <- [0..n]] and bottomHalf = reverse $ drop 0 topHalf) function and in the second example, we are going to use, (diamondStarPattern n = mapM_ putStrLn $ bottomRows ++ topRows where topRows = [spaces i ++ stars (n - 2 * i) | i <- [0..n `div` 2]] and bottomRows = reverse [spaces i ++ stars (n - 2 * i) | i <- [1..n `div` 2]]) function.

Algorithm

• Step 1 ? The diamondStarPattern function is defined using mapM_ and reverse functions

• Step 2 ? The program execution will be started from main function. The main() function has whole control of the program.

• Step 3 ? The resultant diamond star pattern is printed to the console, once the function is being called with argument.

Example 1

In this example, the diamond star pattern is printed using unlines and replicate function.

main = do
  let n = 3
  putStrLn $ diamondStarPattern n

diamondStarPattern :: Int -> String
diamondStarPattern n = unlines $ topHalf ++ bottomHalf
  where topHalf = [replicate (n - i) ' ' ++ replicate ((2 * i) - 1) '*' | i <- [0..n]]
        bottomHalf = reverse $ drop 0 topHalf

Output

  [1 of 1] Compiling Main             ( main.hs, main.o )
Linking main ...
   
  *
 ***
*****
*****
 ***
  * 

Example 2

In this example, the diamond star pattern is printed using mapM_ and reverse function.

diamondStarPattern :: Int -> IO ()
diamondStarPattern n = mapM_ putStrLn $  bottomRows ++ topRows
  where
    topRows = [spaces i ++ stars (n - 2 * i) | i <- [0..n `div` 2]]
    bottomRows = reverse [spaces i ++ stars (n - 2 * i) | i <- [1..n `div` 2]]
    stars x = replicate x '*'
    spaces x = replicate x ' '

main = diamondStarPattern 7

Output

  [1 of 1] Compiling Main             ( main.hs, main.o )
Linking main ...
   *
  ***
 *****
*******
 *****
  ***
   *

Conclusion

The diamond star pattern is a pattern made up of asterisks (*) arranged in the shape of a diamond. The pattern consists of two parts - an upper triangle and a lower triangle. The upper triangle is formed by a series of lines that gradually decrease in length from the center until they meet at a point at the top. The lower triangle is formed by a series of lines that gradually increase in length from the center until they reach the maximum width at the bottom. The two triangles are separated by a single line of asterisks. The overall effect is a diamond shape with a star pattern.