單鏈表的輸出，逆序，排序

ListNode節點的定義

template<class T>
struct ListNode {
	T val;
	ListNode* next;
	ListNode(T val) {
		this->val = val;
		this->next = nullptr;
	}
};

鏈表的幾個簡單的題目

/*從文件中讀取鏈表數據*/
template<class T>
ListNode<T>* readLinkedList(const char* fileName) {
	ListNode<T>* list = new ListNode<T>(NULL);
	ListNode<T>* dummyList = list;
	T tempVal = NULL;
	std::ifstream fin(fileName);
	if (fin.is_open()) {
		char tempChar;
		while (fin >> tempChar && tempChar != ']') {
			fin >> tempVal;
			list->next = new ListNode<T>(tempVal);
			list = list->next;
		}
		fin.close();
	}
	tempVal = NULL;
	return dummyList->next;
}

/*合併兩個非遞減鏈表爲非遞增鏈表*/
// 合併到l1上
template<class T>
ListNode<T>* mergeTwoSortedList(ListNode<T>* l1, ListNode<T>* l2) {
	if (l1 == nullptr) {
		return reverseLinkedList(l2);
	}
	if (l2 == nullptr) {
		return reverseLinkedList(l1);
	}
	if (l1 != nullptr && l2 != nullptr) {
		ListNode<T>* p1 = l1;
		ListNode<T>* p2 = l2;
		// 使l1的頭節點爲最小值
		if (l1->val > l2->val) {
			p2 = l2->next;
			l2->next = l1;
			l1 = l2;
			l2 = p2;
			p1 = l1;
		}
		while (p1->next != nullptr && p2->next != nullptr) {
			if (p1->val <= p2->val && p2->val <= p1->next->val) {
				p2 = l2->next;
				l2->next = p1->next;
				p1->next = l2;
				l2 = p2;
				p1 = p1->next;
			}
			else {
				p1 = p1->next;
			}
		}
		while (p1->next != nullptr) {
			p1 = p1->next;
		}
		if (p1->val <= p2->val) {
			p1->next = p2;
		}
	}
	return reverseLinkedList(l1);
}

/*鏈表逆序*/
template<class T>
ListNode<T>* reverseLinkedList(ListNode<T>* head) {
	if (head == nullptr || head->next == nullptr) {
		return head;
	}
	ListNode<T>* prev = head;
	ListNode<T>* curr = head->next;
	ListNode<T>* next = head;
	while (curr != nullptr) {
		next = curr->next;
		curr->next = prev;
		prev = curr;
		curr = next;
	}
	head->next = nullptr;
	return prev;
}

/*順序輸出鏈表*/
template<class T>
void outputLinkedList(ListNode<T>* head, std::ofstream &fout) {
	if (head != nullptr) {
		fout << head->val << '\t';
		outputnextedList(head->next, fout);
	}
}

/*逆序輸出鏈表*/
template<class T>
void reverseOutputLinkedList(ListNode<T>* head, std::ofstream &fout) {
	if (head != nullptr) {
		reverseOutputnextedList(head->next, fout);
		fout << head->val << '\t';
	}
}