原题链接: https://oj.leetcode.com/problems/linked-list-cycle-ii/

public ListNode detectCycle(ListNode head) {
    if (head == null) return null;

    ListNode slowCursor = head;
    ListNode quickCursor = head;
    boolean hasCycle = false;

    while (quickCursor != null && quickCursor.next!=null) {
        slowCursor = slowCursor.next;
        quickCursor = quickCursor.next.next;

        if (slowCursor == quickCursor) {
            hasCycle = true;

            break;
        }
    }

    if (!hasCycle) return null;

    // reset either reference to head
    slowCursor = head;

    // iterate again until both references meet again, then getting the wanted node
    while (slowCursor != quickCursor) {
        slowCursor = slowCursor.next;
        quickCursor = quickCursor.next;
    }

    return slowCursor;
}