142. 环形链表 II #
题目地址 #
解题思路 #
具体实现 #
```go
package main
import "fmt"
type ListNode struct {
Val int
Next *ListNode
}
func detectCycle(head *ListNode) *ListNode {
if head == nil {
return head
}
low, fast := head, head
// 因为快指针走 2 步，不要判断 next 是否为 nil
for fast != nil && fast.Next != nil {
low = low.Next
fast = fast.Next.Next // 注意这里 fast 是走 2 步
if fast == low {
for low != head {
low = low.Next
head = head.Next
}
return head
}
}
return nil
}
func main() {
index2 := &ListNode{
Val: 101,
Next: nil,
}
index := &ListNode{
Val: 100,
Next: index2,
}
index.Next.Next = &ListNode{
Val: 4,
Next: index,
}
fmt.Println(detectCycle(&ListNode{
Val: 1,
Next: &ListNode{
Val: 2,
Next: &ListNode{
Val: 3,
Next: index,
},
},
}))
}
```