u

top-100-liked/25/25_test.go

@@ -0,0 +1,58 @@
+package top100liked
+
+import (
+	"fmt"
+	"testing"
+)
+
+// https://leetcode.cn/problems/linked-list-cycle/description/?envType=study-plan-v2&envId=top-100-liked
+
+type ListNode struct {
+	Val  int
+	Next *ListNode
+}
+
+// func hasCycle(head *ListNode) bool {
+// 	_map := make(map[*ListNode]bool)
+// 	for head != nil {
+// 		if _map[head] {
+// 			return true
+// 		}
+// 		_map[head] = true
+// 		head = head.Next
+// 	}
+// 	return false
+// }
+
+func hasCycle(head *ListNode) bool {
+	if head == nil || head.Next == nil {
+		return false
+	}
+	slow, fast := head, head.Next
+	for fast != slow {
+		if fast == nil || fast.Next == nil {
+			return false
+		}
+		slow = slow.Next
+		fast = fast.Next.Next
+	}
+	return true
+}
+
+func TestS24(t *testing.T) {
+	input := &ListNode{
+		Val: 3,
+		Next: &ListNode{
+			Val: 2,
+			Next: &ListNode{
+				Val: 0,
+				Next: &ListNode{
+					Val:  -4,
+					Next: nil,
+				},
+			},
+		},
+	}
+	input.Next.Next.Next.Next = input.Next
+	fmt.Println(hasCycle(input))
+}