add: 环形链表

src/list/linked-list-cycle.js

@@ -0,0 +1,28 @@
+/**
+ * Definition for singly-linked list.
+ * function ListNode(val) {
+ *     this.val = val;
+ *     this.next = null;
+ * }
+ */
+
+/**
+ * @param {ListNode} head
+ * @return {boolean}
+ */
+export const hasCycle = function (head) {
+  if (!head || !head.next) return false
+
+  // 双指针解法
+  let slow = head
+  let fast = head.next
+
+  while (true) {
+    if (!fast || !fast.next) return false
+    else if (fast.next === slow || fast === slow) return true
+    else {
+      fast = fast.next.next
+      slow = slow.next
+    }
+  }
+}