- Added guest contributions by Laurent Rosenfeld.

2 files changed, 64 insertions, 0 deletions

diff --git a/challenge-147/laurent-rosenfeld/ring/ch-1.ring b/challenge-147/laurent-rosenfeld/ring/ch-1.ring
new file mode 100644
index 0000000000..578e9db72c
--- /dev/null
+++ b/challenge-147/laurent-rosenfeld/ring/ch-1.ring
@@ -0,0 +1,43 @@
+max = 20
+primes = [2, 3, 5]
+primes_h = []
+count = len(primes)
+for i = 1 to count
+    primes_h[string(primes[i])] = i
+next
+truncatables = primes
+candidate = primes[count]
+while count < max
+    candidate += 2
+    not_prime = false
+    pos = substr(string(candidate), "0")
+    if pos > 0 loop ok
+    sq_cand = floor(sqrt(candidate))
+    for i in primes
+        if candidate % i = 0
+            not_prime = true
+            exit
+        ok
+        if i > sq_cand exit ok
+    next
+    if not_prime loop ok
+    add (primes, candidate)
+    primes_h[string(candidate)] = 1
+    // We've found a prime, now check if truncatable prime
+    length = len(string(candidate))
+    is_truncatable = true
+    for i = 1 to length
+        truncated = right(string(candidate), i)
+        if isnull(primes_h[truncated])
+            is_truncatable = false
+            exit
+        ok
+    next
+    if is_truncatable
+        add(truncatables, candidate);
+        count += 1
+    ok
+
+end
+for val in truncatables see "" + val + " " next
+see " " + nl
diff --git a/challenge-147/laurent-rosenfeld/ring/ch-2.ring b/challenge-147/laurent-rosenfeld/ring/ch-2.ring
new file mode 100644
index 0000000000..b5bd69f2a6
--- /dev/null
+++ b/challenge-147/laurent-rosenfeld/ring/ch-2.ring
@@ -0,0 +1,21 @@
+max = 3000
+pentanums = []
+for i = 1 to max
+    add (pentanums,  i * (3 * i - 1) / 2)
+next
+// see pentanums + nl
+penta_h = []
+for i = 1 to max
+    penta_h[ string(pentanums[i])] = i
+next
+for i = 1 to max
+    for j = i+1 to max
+        diff = pentanums[j] - pentanums[i]
+        diff_s = string(diff)
+        if isnull(penta_h[diff_s]) loop ok
+        sum = pentanums[i] + pentanums[j]
+        sum_s = string(sum)
+        if isnull(penta_h[sum_s]) loop ok
+        see "" + diff + " " + sum + " " + pentanums[i] + " " + pentanums[j] + nl
+    next
+next