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:

	int GetListLength(ListNode *list) {
		int result = 0;
		while (list != nullptr) {
			list = list->next;
			result++;
		}
		return result;
	}

    ListNode* FindFirstCommonNode( ListNode* pHead1, ListNode* pHead2) {
		
		ListNode *l = pHead1, *r = pHead2;

		int left = GetListLength(l);
		int right = GetListLength(r);

		l = pHead1;
		r = pHead2;

		int diff = abs(left-right);
		if (left < right) {
			ListNode* tmp = l;
			l = r;
			r = tmp;
		}

		while (diff > 0) {
			l = l->next;
			diff--;
		}

		while (l != nullptr && r != nullptr) {
			if (l == r) {
				return l;
			}
			l = l->next;
			r = r->next;
		}

		return nullptr;
	}
};