add 287-Find-the-Duplicate-Number

Author: loczek

javascript/287-Find-the-Duplicate-Number.js

@@ -0,0 +1,24 @@
+function findDuplicate(nums) {
+  let slow = 0;
+  let fast = 0;
+
+  while (true) {
+    slow = nums[slow];
+    fast = nums[nums[fast]];
+    if (slow == fast) {
+      break;
+    }
+  }
+
+  let slow2 = 0;
+
+  while (true) {
+    slow = nums[slow];
+    slow2 = nums[slow2];
+    if (slow == slow2) {
+      break;
+    }
+  }
+
+  return slow;
+}