LeetCode 141:环形链表

题目：

题解：

代码示例：

package com.zy.leetcode.LeetCode_141;

/**
 * @Author: zy
 * @Date: 2025-01-03-14:09
 * @Description: 环形链表
 */
public class ListNode_141 {

    private int val;

    private ListNode_141 next;

    public ListNode_141(int x) {
        val = x;
        next = null;
    }

    public static ListNode_141 createList(int[] arr) {
        ListNode_141 dummy = new ListNode_141(0);
        ListNode_141 cur = dummy;
        for (int num : arr) {
            cur.next = new ListNode_141(num);
            cur = cur.next;
        }
        return dummy.next;
    }

    public static void printList(ListNode_141 head) {
        ListNode_141 cur = head;
        while (cur != null) {
            System.out.print(cur.val + " -> ");
            cur = cur.next;
        }
        System.out.println("null");
    }

    /**
     * t兔子一次走两步
     * 龟一次走一步
     *
     * @param node
     * @return
     */
    private static boolean hasCycle(ListNode_141 node) {
        ListNode_141 h = node;//兔
        ListNode_141 t = node;// tortoise

        while (h != null && h.next != null) {
            h = h.next.next;
            t = t.next;
            if (h == t) {
                return true;
            }
        }
        return false;
    }

    public static void main(String[] args) {
        int[] arr = {3, 2, 0, -4, 9, 5};
        ListNode_141 head = createList(arr);
        printList(head);

        System.out.println(hasCycle(head)); // true

        //环行链表
        ListNode_141 node1 = new ListNode_141(3);
        ListNode_141 node2 = new ListNode_141(2);
        ListNode_141 node3 = new ListNode_141(0);
        ListNode_141 node4 = new ListNode_141(-4);
        ListNode_141 node5 = new ListNode_141(9);
        ListNode_141 node6 = new ListNode_141(5);

        node1.next = node2;
        node2.next = node3;
        node3.next = node4;
        node4.next = node5;
        node5.next = node6;
        node6.next = node2;

        System.out.println(hasCycle(node1)); // true

    }
}