solved: 142

Author: ryoppippi

code/142.linked-list-cycle-ii.ts

@@ -0,0 +1,38 @@
+  // class ListNode {
+  //     val: number
+  //     next: ListNode | null
+  //     constructor(val?: number, next?: ListNode | null) {
+  //         this.val = (val===undefined ? 0 : val)
+  //         this.next = (next===undefined ? null : next)
+  //     }
+  // }
+// @leet start
+/**
+ * Definition for singly-linked list.
+ * class ListNode {
+ *     val: number
+ *     next: ListNode | null
+ *     constructor(val?: number, next?: ListNode | null) {
+ *         this.val = (val===undefined ? 0 : val)
+ *         this.next = (next===undefined ? null : next)
+ *     }
+ * }
+ */
+
+function detectCycle(_head: ListNode | null): ListNode | null {
+  const prevVisited = new Set<ListNode>();
+
+  let head = _head;
+
+  while (head) {
+    if (prevVisited.has(head)) {
+      return head;
+    }
+
+    prevVisited.add(head);
+    head = head.next;
+  }
+
+  return null;
+};
+// @leet end