path: root/challenge-079/richard-park/apl/ch-2.aplf

 TrappedRainWater←{
     +/⌈\-⊢             ⍝ Elegant train
⍝    +/⍵-⍨+/∨⍀⍵∘.≥⍳⌈/⍵  ⍝ From the video
⍝    +/                 Sum of
⍝      ⍵-⍨              bottom of buckets
⍝         +/∨⍀          to top of buckets
⍝             ⍵∘.≥⍳⌈/⍵  in a histogram rep. of ⍵
 }