From 3531cc83e5609d9a827b954b4bb017bd1124ccbc Mon Sep 17 00:00:00 2001
From: Mohammad S Anwar <mohammad.anwar@yahoo.com>
Date: Sun, 25 Apr 2021 03:20:59 +0100
Subject: - Added guest contributions by Laurent Rosenfeld.

---
 challenge-109/laurent-rosenfeld/lua/ch-2.lua | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)
 create mode 100644 challenge-109/laurent-rosenfeld/lua/ch-2.lua

(limited to 'challenge-109/laurent-rosenfeld/lua/ch-2.lua')

diff --git a/challenge-109/laurent-rosenfeld/lua/ch-2.lua b/challenge-109/laurent-rosenfeld/lua/ch-2.lua
new file mode 100644
index 0000000000..e972de6a62
--- /dev/null
+++ b/challenge-109/laurent-rosenfeld/lua/ch-2.lua
@@ -0,0 +1,20 @@
+local function check_square (p)
+    sum = p[1] + p[2]
+    return p[2] + p[3] + p[4] == sum and
+        p[4] + p[5] + p[6] == sum and
+        p[6] + p[7] == sum
+end
+
+local function permute(perm, n)
+    if n == 0  and check_square(perm) then
+        print( table.concat(perm, ' ') )
+    else
+        for i = 1, n do
+            perm[i], perm[n] = perm[n], perm[i]
+            permute(perm, n - 1)
+            perm[i], perm[n] = perm[n], perm[i]
+        end
+    end
+end
+
+permute({1,2,3,4,5,6,7}, 7)
-- 
cgit