Solutions for challenge #147

1 files changed, 41 insertions, 0 deletions

diff --git a/challenge-147/roger-bell-west/javascript/ch-2.js b/challenge-147/roger-bell-west/javascript/ch-2.js
new file mode 100755
index 0000000000..8d55a5edde
--- /dev/null
+++ b/challenge-147/roger-bell-west/javascript/ch-2.js
@@ -0,0 +1,41 @@
+#! /usr/bin/node
+
+function pentagon(n) {
+    return Math.floor(n*(3*n-1)/2);
+}
+
+function pentpair() {
+    let fpent=[0];
+    let rpent=new Map();
+    let mx=0;
+    let a=1;
+    while (true) {
+        while (mx < a) {
+            mx++;
+            fpent.push(pentagon(mx));
+            rpent.set(fpent[mx],mx);
+        }
+        for (b = 1; b < a; b++) {
+            let d=fpent[a]-fpent[b];
+            if (d < fpent[b]) {
+                break;
+            }
+            if (rpent.has(d)) {
+                let s=fpent[a]+fpent[b];
+                while (s > fpent[mx]) {
+                    mx++;
+                    fpent.push(pentagon(mx));
+                    rpent.set(fpent[mx],mx);
+                }
+                if (rpent.has(s)) {
+                    console.log("P(%d) + P(%d) = %d + %d = %d = P(%d)",a,b,fpent[a],fpent[b],s,rpent.get(s));
+                    console.log("P(%d) - P(%d) = %d - %d = %d = P(%d)",a,b,fpent[a],fpent[b],d,rpent.get(d));
+                    throw '';
+                }
+            }
+        }
+        a++;
+    }
+}
+
+pentpair();