Merge pull request #5497 from Firedrake/rogerbw-challenge-147

Solutions for challenge #147

1 files changed, 39 insertions, 0 deletions

diff --git a/challenge-147/roger-bell-west/python/ch-2.py b/challenge-147/roger-bell-west/python/ch-2.py
new file mode 100755
index 0000000000..b524b7e5e5
--- /dev/null
+++ b/challenge-147/roger-bell-west/python/ch-2.py
@@ -0,0 +1,39 @@
+#! /usr/bin/python3
+
+def pentagon(n):
+  return int(n*(3*n-1)/2)
+
+def pentpair():
+  fpent=[0]
+  rpent=dict()
+  mx=0
+  a=1
+  while 1:
+    while mx < a:
+      mx += 1
+      fpent.append(pentagon(mx))
+      rpent[fpent[mx]]=mx
+    for b in range(1,a):
+      d=fpent[a]-fpent[b]
+      if d in rpent:
+        s=fpent[a]+fpent[b]
+        while s > fpent[mx]:
+          mx += 1
+          fpent.append(pentagon(mx))
+          rpent[fpent[mx]]=mx
+        if s in rpent:
+          print("P({:d}) + P({:d}) = {:d} + {:d} = {:d} = P({:d})".format(
+            a, b,
+            fpent[a], fpent[b],
+            s,
+            rpent[s]))
+          print("P({:d}) - P({:d}) = {:d} - {:d} = {:d} = P({:d})".format(
+            a, b,
+            fpent[a], fpent[b],
+            d,
+            rpent[d]))
+          quit()
+    a += 1
+          
+
+pentpair()