Intersection of Two Linked Lists

 public ListNode GetIntersectionNode(ListNode headA, ListNode headB) {
        
       var pointA = headA;
        var pointB = headB;
        if(headA != null && headB != null) {
            while(pointA != pointB) {
                if(pointA == null) {
                    pointA = headB;
                } else {
                    pointA = pointA.next;
                }
                if(pointB == null) {
                    pointB = headA;
                } else {
                    pointB = pointB.next;
                }
                if((pointA == null) && (pointB == null)) {
                    return null;
                }
            }
            return pointA;
        } else {
            return null;
        }
 
    }
或者 等同于
if (headA == null || headB == null)
                return null;
            ListNode currA = headA;
            ListNode currB = headB;
            while (currA!=currB)
            {
                currA = currA == null ? headB : currA.next;
                currB = currB == null ? headA : currB.next;
            }
            return currA;

 private static ListNode GetIntersectionNode2(ListNode headA, ListNode headB) {
        var nodeA = headA;
        var nodeB = headB;
        var set = new HashSet<ListNode>();
        while(nodeA != null) {
            set.Add(nodeA);
            nodeA = nodeA.next;
        }
        while(nodeB != null) {
            if(set.Contains(nodeB)) {
                return nodeB;
            }
            nodeB = nodeB.next;
        }
        return null;
    }