两个链表的第一个公共节点

方式一：
public ListNode findFirstCommonNode(ListNode pHead1, ListNode pHead2) {
	ListNode p1 = pHead1;
	ListNode p2 = pHead2;
	while(p1 != p2) {
		p1 = p1 == null ? pHead2 : p1.next;
		p2 = p2 == null ? pHead1 : p2.next;
	}
	return p1;
}
方式二：
public ListNode FindFirstCommonNode(ListNode pHead1, ListNode pHead2) {
	ListNode curr1 = pHead1;
	ListNode curr2 = pHead2;
	Map map = new HashMap<>();
	while (curr1 != null) {
		map.put(curr1, null);
		curr1 = curr1.next;
	}
	while(curr2 != null) {
		if (map.containsKey(curr2)) {
			return curr2;
		}
		curr2 = curr2.next;
	}
	return null;
}