Data update

Task/De-Bruijn-sequences/JavaScript/de-bruijn-sequences.js

@@ -0,0 +1,96 @@
+function deBruijn(k, n) {
+  const a = new Array(k * n).fill(0);
+  const seq = [];
+
+  function db(t, p) {
+    if (t > n) {
+      if (n % p === 0) {
+        for (let i = 1; i < p + 1; i++) {
+          seq.push(a[i]);
+        }
+      }
+    } else {
+      a[t] = a[t - p];
+      db(t + 1, p);
+      let j = a[t - p] + 1;
+      while (j < k) {
+        a[t] = j & 0xFF;
+        db(t + 1, t);
+        j++;
+      }
+    }
+  }
+
+  db(1, 1);
+  let buf = "";
+  for (const i of seq) {
+    buf += String(i);
+  }
+  return buf + buf.substring(0, n - 1);
+}
+
+function allDigits(s) {
+  for (const c of s) {
+    if (c < '0' || '9' < c) {
+      return false;
+    }
+  }
+  return true;
+}
+
+function validate(db) {
+  const le = db.length;
+  const found = new Array(10000).fill(0);
+  const errs = [];
+
+  // Check all strings of 4 consecutive digits within 'db'
+  // to see if all 10,000 combinations occur without duplication.
+  for (let i = 0; i < le - 3; i++) {
+    const s = db.substring(i, i + 4);
+    if (allDigits(s)) {
+      const n = parseInt(s);
+      found[n]++;
+    }
+  }
+
+  for (let i = 0; i < 10000; i++) {
+    if (found[i] === 0) {
+      errs.push(`    PIN number ${i} missing`);
+    } else if (found[i] > 1) {
+      errs.push(`    PIN number ${i} occurs ${found[i]} times`);
+    }
+  }
+
+  if (errs.length === 0) {
+    console.log("  No errors found");
+  } else {
+    const pl = (errs.length === 1) ? "" : "s";
+    console.log(`  ${errs.length} error${pl} found:`);
+    for (const e of errs) {
+      console.log(e);
+    }
+  }
+}
+
+function main() {
+  const db = deBruijn(10, 4);
+
+  console.log(`The length of the de Bruijn sequence is ${db.length}\n`);
+  console.log("The first 130 digits of the de Bruijn sequence are: " + db.substring(0, 130));
+  console.log("\nThe last 130 digits of the de Bruijn sequence are: " + db.substring(db.length - 130));
+  console.log("\n");
+
+  console.log("Validating the de Bruijn sequence:");
+  validate(db);
+
+  console.log("\nValidating the reversed de Bruijn sequence:");
+  const rdb = db.split("").reverse().join("");
+  validate(rdb);
+
+  const by = db.split("");
+  by[4443] = '.';
+  console.log("\nValidating the overlaid de Bruijn sequence:");
+  validate(by.join(""));
+}
+
+main();