Linked List Cycle
Given a linked list, determine if it has a cycle in it.
Follow up:
Can you solve it without using extra space?
SOLUTION 1:
经典快慢指针问题。如果存在环,fast, slow必然会相遇。就像2个速度不一样的人在环形跑道赛跑,总有一个时间他们会相遇。
如果fast到达了null,就是没有环,可以返回false.
package Algorithms.list; import Algorithms.algorithm.others.ListNode; /**
* Definition for singly-linked list.
* class ListNode {
* int val;
* ListNode next;
* ListNode(int x) {
* val = x;
* next = null;
* }
* }
*/
public class HasCycle {
public boolean hasCycle(ListNode head) {
if (head == null) {
return false;
} ListNode slow = head;
ListNode fast = head; while (fast != null && fast.next != null) {
slow = slow.next;
fast = fast.next.next;
if (slow == fast) {
return true;
}
} return false;
}
}