LeetCode/com/zerroi/leetcode/Three22/HasCycle.java

package com.zerroi.leetcode.Three22;

public class HasCycle {
    public static void main(String[] args) {
        ListNode l1 = new ListNode(1);
        ListNode l2 = new ListNode(1);
        l1.next = l2;
        SolutionThird solutionThird = new SolutionThird();
        boolean res = solutionThird.hasCycle(l1);
        System.out.println("res = " + res);
    }
}

class SolutionThird {
    public boolean hasCycle(ListNode head) {
        if (head.next == null) return false;
        ListNode slow = head;
        ListNode fast = head;
        while (fast.next != null) {
            slow = slow.next;
            fast = fast.next.next;
            if (slow == fast) {
                return true;
            }
        }
        return false;
    }
}

class ListNode {
    int val;
    ListNode next;
    ListNode(int x) {
        val = x;
        next = null;
    }
}