题解 | #牛牛的冒险旅程#

哈希表+gcd

import java.util.*;

public class Solution {
    public int gcdInCycle (ListNode head) {
        // write code here
        Set<Integer> set = new HashSet<>();
        int g = 0;
        while (head != null) {
            if (set.contains(head.val)) g = gcd(g, head.val);
            set.add(head.val);
            head = head.next;
        }
        return g == 0 ? -1 : g;
    }
    int gcd(int a, int b) {
        return a % b == 0 ? b : gcd(b, a % b);
    }
}