Given a linked list, determine if it has a cycle in it.
Follow up:
Can you solve it without using extra space?
题意:判断链表是否成环。
注意:最后一个节点的next指针,有可能指向链表中任意一个节点
方法一:使用HashSet,保存遍历过的节点的HashCode
public class Solution {
public bool HasCycle(ListNode head) {
if (head == null) {
return false;
}
ListNode node = head;
HashSet<int> hashSet = new HashSet<int>();
hashSet.Add(node.GetHashCode());
while (node.next != null) {
node = node.next;
int hash = node.GetHashCode();
if (hashSet.Contains(hash)) {
return true;
} else {
hashSet.Add(hash);
}
}
return false;
}
}
方法二:使用两个指针,一个快一个慢,如果两个指针相遇,则链表成环
public class Solution {
public bool HasCycle(ListNode head) {
if (head == null || head.next == null) {
return false;
}
ListNode slow = head;
ListNode fast = head;
while (fast.next != null && fast.next.next != null) {
slow = slow.next;
fast = fast.next.next;
if (slow == fast) {
return true;
}
}
return false;
}
}