add old solutions

1 files changed, 13 insertions, 0 deletions

diff --git a/15.lua b/15.lua
new file mode 100644
index 0000000..8450302
--- /dev/null
+++ b/15.lua
@@ -0,0 +1,13 @@
+function combinations(n, r)
+    local numerator = 1
+    local denominator = 1
+    for i = n, n - r + 1, -1 do
+        numerator = numerator * i
+    end
+    for i = r, 1, -1 do
+        denominator = denominator * i
+    end
+    return numerator / denominator
+end
+
+print(combinations(40, 20))