challenge-067/richard-park/apl/NumberCombinations.aplf


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 NumberCombinations←{
⍝ ←: All strictly ascending vectors of length ⍵ 
⍝    which contain numbers in ⍳⍺
⍝ Attempt 1
⍝ =========
     c←,((⍳⍺)∘.,⊢)⍣(¯1+⍵)⊢⍳⍺       ⍝ All combinations of digits in (⍳⍺)
                                   ⍝ Of length ⍵
     c⌿⍨{((∪≡⊢)⍵)∧((⊂⍋⍵)⌷⍵)≡⍵}¨c   ⍝ Strictly ascending combinations
⍝ Attempt 2
⍝ =========
⍝ e.g. 5 NumberCombinations 2
     a←⍳¯1+⍺   
     b←(¯1+⍺)⍴⊂a     ⍝ Maximal run repeated ¯1+⍺ times
     c←1+0~⍨¨b×a≤b   ⍝ Remove 0s and add 1
     ⊃,/a,¨¨c        ⍝ Catenate a's with c's 
 }