LeetCode -- Linked List cycle

LeetCode -- Linked List cycle

本題描述：


Given a linked list, determine if it has a cycle in it.


Follow up:
Can you solve it without using extra space?


檢測鏈表中是否有環。


思路：
經典算法，使用快慢指針，快的一次走兩步，慢的一次走一步，如果有環它們一定會相遇。


實現代碼：

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     public int val;
 *     public ListNode next;
 *     public ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    
    public bool HasCycle(ListNode head) {
        if(head == null){
    		return false;
    	}
    	
    	var p = head;
    	var q = head;


    	while(p != null && q != null && q.next != null){
    		var t = q;
    		p = p.next;
    		q = q.next.next;
    		if(ReferenceEquals(p,q)){
    			return true;
    		}
    	}
    	return false;
    }
}