2 files changed, 25 insertions, 0 deletions
diff --git a/challenge-308/richard-park/apl/CountCommon.aplf b/challenge-308/richard-park/apl/CountCommon.aplf
new file mode 100644
index 0000000000..ac2d5a17e2
--- /dev/null
+++ b/challenge-308/richard-park/apl/CountCommon.aplf
@@ -0,0 +1,10 @@
+ CountCommon←{
+⍝ Can be defined as the 2-train atop
+     CountCommon←≢∩
+⍝ Literally "count the intersection"
+⍝             ≢             ∩
+⍝ Example
+⍝       'perl' 'weekly' 'challenge' (≢∩) 'raku' 'weekly' 'challenge'
+⍝ 2
+     ≢⍺∩⍵
+ }
diff --git a/challenge-308/richard-park/apl/DecodeXOR.aplf b/challenge-308/richard-park/apl/DecodeXOR.aplf
new file mode 100644
index 0000000000..a2c2cb7b2b
--- /dev/null
+++ b/challenge-308/richard-park/apl/DecodeXOR.aplf
@@ -0,0 +1,15 @@
+ DecodeXOR←{
+⍝ ⍺: initial
+⍝ ⍵: encoded sequence
+⍝ ←: original array that produced ⍵
+⍝    ⍵ ← 2{2⊥≠/2⊥⍣¯1⊢⍵}/original
+     0∊⍴⍵:⍺
+     nxt←2⊥≠/2⊥⍣¯1⊢⍺,⊃⍵
+     ⍺,nxt ∇ 1↓⍵
+
+⍝ Examples:
+⍝       1 DecodeXOR 1 2 3
+⍝ 1 0 2 1
+⍝       4 DecodeXOR 6 2 7 3
+⍝ 4 2 0 7 4
+ }