Introduction Link to heading
Given a linked list, determine if it has a cycle in it.
To represent a cycle in the given linked list, we use an integer pos which represents the position (0-indexed) in the linked list where tail connects to. If pos is -1, then there is no cycle in the linked list.
Example 1:
Input: head = [3,2,0,-4], pos = 1
Output: true
Explanation: There is a cycle in the linked list, where tail connects to the second node.
Example 2:
Input: head = [1,2], pos = 0
Output: true
Explanation: There is a cycle in the linked list, where tail connects to the first node.
Example 3:
Input: head = [1], pos = -1
Output: false
Explanation: There is no cycle in the linked list.
Follow up: Link to heading
Can you solve it using O(1) (i.e. constant) memory?
Solution Link to heading
Simple solution:
type ListNode struct {
Val int
Next *ListNode
}
func hasCycle(head *ListNode) bool {
if head == nil {
return false
}
for i, j := one(head), two(head); i != nil && j != nil; i, j = one(i), two(j) {
if i == j {
return true
}
}
return false
}
func one(node *ListNode) *ListNode {
return node.Next
}
func two(node *ListNode) *ListNode {
next := node.Next
if next == nil {
return nil
} else {
return next.Next
}
}
Explanation Link to heading
We need two pointers, i will do one step a time, j will do two steps a time. We have cycle only if they meet each other.