题解 | #两个链表的第一个公共结点#

/*
struct ListNode {
	int val;
	struct ListNode *next;
	ListNode(int x) :
			val(x), next(NULL) {
	}
};*/
class Solution {
public:
    ListNode* FindFirstCommonNode( ListNode* pHead1, ListNode* pHead2) {
		if (!pHead1 || !pHead2) {
			return nullptr;
		}
        ListNode* p1 = pHead1;
		ListNode* p2 = pHead2;
		while (p1 && p2) {
			if (p1 == p2) {
				return p1;
			}
			p1 = p1->next;
			p2 = p2->next;
		}
		if (p1) {
			ListNode* new_p1 = pHead1;
			while (p1) {
				new_p1 = new_p1->next;
				p1 = p1->next;
			}
			ListNode* new_p2 = pHead2;
			while (new_p1 && new_p2) {
				if (new_p1 == new_p2) {
					return new_p1;
				}
				new_p1 = new_p1->next;
				new_p2 = new_p2->next;
			}
		} 
		if (p2) {
			ListNode* new_p2 = pHead2;
			while (new_p2 && p2) {
				new_p2 = new_p2->next;
				p2 = p2->next;
			}
			ListNode* new_p1 = pHead1;
			while (new_p1 && new_p2) {
				if (new_p1 == new_p2) {
					return new_p1;
				}
				new_p1 = new_p1->next;
				new_p2 = new_p2->next;
			}
		}

		return nullptr;
    }
};