p26

inputs/passing/projEuler/p26.ts

@@ -0,0 +1,53 @@
+export default function () {
+  let longestCycle = 0;
+  let longestCycleN = 0;
+
+  for (let n = 2; n < 1_000; n++) {
+    const cycleLen = reciprocalDigitsData(n).cycle.length;
+
+    if (cycleLen > longestCycle) {
+      longestCycle = cycleLen;
+      longestCycleN = n;
+    }
+  }
+
+  return longestCycleN;
+}
+
+function reciprocalDigitsData(n: number) {
+  let digits: number[] = [];
+
+  let rems: number[] = [10];
+  let rem = 10;
+
+  while (true) {
+    const digit = Math.floor(rem / n);
+    rem -= digit * n;
+    rem *= 10;
+    digits.push(digit);
+
+    if (rems.includes(rem)) {
+      break;
+    }
+
+    rems.push(rem);
+  }
+
+  let head = "";
+
+  const cycleRem = rem;
+  rem = 10;
+
+  while (rem !== cycleRem) {
+    const digit = Math.floor(rem / n);
+    rem -= digit * n;
+    rem *= 10;
+
+    head += digits.shift();
+  }
+
+  return {
+    head,
+    cycle: digits.join(""),
+  };
+}