Algorithms: No Repeats Please

Algorithms/noRepeatsPlease.js

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+// https://www.freecodecamp.org/learn/coding-interview-prep/algorithms/no-repeats-please
+
+function permAlone(str) {
+  let noRepeatsCount = 0;
+  noRepeatsCount += Number(!/(.{1})\1/.test(str));
+
+  function swap(Arr, iA, iB) {
+    const tmp = Arr[iA];
+    Arr[iA] = Arr[iB];
+    Arr[iB] = tmp;
+  }
+
+  const strArr = str.split("");
+  const strLength = strArr.length;
+  // Heap's Algorithm as explained @ https://www.baeldung.com/cs/array-generate-all-permutations
+  const c = Array(strLength).fill(0);
+  let i = 0;
+  while (i < strLength) {
+    if (c[i] < i) {
+      if (i % 2) {
+        swap(strArr, c[i], i);
+      } else {
+        swap(strArr, 0, i);
+      }
+      noRepeatsCount += Number(!/(.{1})\1/.test(strArr.join("")));
+      c[i]++;
+      i = 0;
+    } else {
+      c[i] = 0;
+      i++;
+    }
+  }
+
+  return noRepeatsCount;
+}
+
+console.log(permAlone("abcdefa"));