Cycle Detection: Floyd's The Tortoise and the The Hare

cycle-detection-floyds-the-tortoise-and-the-the-hare/index.js

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+// https://www.codewars.com/kata/cycle-detection-floyds-the-tortoise-and-the-the-hare/javascript
+
+const floyd = function(f, x0) {
+  let x = x0;
+  let i = 0;
+  const map = new WeakMap();
+  
+  while (1) {
+    map[x] = i++;
+    x = f(x);
+    if (x in map) break;
+  }
+  
+  return  [map[x], i - map[x]];
+}