Create 142-linked-list-cycle-ii.js

Author: everthis

142-linked-list-cycle-ii.js

@@ -0,0 +1,30 @@
+/**
+ * Definition for singly-linked list.
+ * function ListNode(val) {
+ *     this.val = val;
+ *     this.next = null;
+ * }
+ */
+
+/**
+ * @param {ListNode} head
+ * @return {ListNode}
+ */
+const detectCycle = function(head) {
+  if(head === null || head.next === null) return null
+  let fast = head
+  let slow = head
+  let start = head
+  while(fast !== null && fast.next !== null) {
+    fast = fast.next.next
+    slow = slow.next
+    if(fast === slow) {
+       while(slow !== start) {
+         slow = slow.next
+         start = start.next
+       }
+       return start
+    }
+  }
+  return null
+};