From 1b69aed5e9e0b500356b40efc235da8ec88d7847 Mon Sep 17 00:00:00 2001
From: Dimitri Lozeve <dimitri@lozeve.com>
Date: Sun, 10 May 2020 14:23:06 +0200
Subject: [PATCH] Solve problem 4 task 1

---
 Contest2020/Contest2020.dyalog              | 10 +++++++++-
 Contest2020/Data/rosalind_revp_2_output.txt |  4 ++--
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/Contest2020/Contest2020.dyalog b/Contest2020/Contest2020.dyalog
index f8b0a23..8a34f02 100644
--- a/Contest2020/Contest2020.dyalog
+++ b/Contest2020/Contest2020.dyalog
@@ -39,10 +39,18 @@
                   urls←('https://www.dyalog.com/'∘,)¨paths
                 ∇
 
-                ∇ r←revp dna
+                ⍝ Test if a DNA string is a reverse palindrome.
+                isrevp←{⍵≡⌽'TAGC'['ATCG'⍳⍵]}
+                ⍝ Generate all subarrays (position, length) pairs, for
+                ⍝ 4 ≤ length ≤ 12.
+                subarrays←{⊃,/(⍳⍵),¨¨3↓¨⍳¨12⌊1+⍵-⍳⍵}
+                ∇ r←revp dna;positions
                   ⍝ 2020 APL Problem Solving Competition Phase II
                   ⍝ Stub function for Problem 4, Task 1 - revp
                   ⍝ Put your code and comments below here
+                  positions←subarrays⍴dna
+                  ⍝ Filter subarrays which are reverse palindromes.
+                  r←↑({isrevp dna[¯1+⍵[1]+⍳⍵[2]]}¨positions)/positions
                 ∇
 
                 ∇ r←sset n
diff --git a/Contest2020/Data/rosalind_revp_2_output.txt b/Contest2020/Data/rosalind_revp_2_output.txt
index 9a0a469..191bad7 100644
--- a/Contest2020/Data/rosalind_revp_2_output.txt
+++ b/Contest2020/Data/rosalind_revp_2_output.txt
@@ -1,4 +1,4 @@
-1  4
+  1  4
   2  4
   3  4
  16  4
@@ -86,4 +86,4 @@
 423 10
 445 10
 422 12
-444 12
\ No newline at end of file
+444 12