单向链表反转

1. 单向链表反转

#include <iostream>
#include <string>
#include <sstream>

using std::cout;
using std::cin;
using std::endl;
using std::string;
using std::ostringstream;

namespace {

struct ListNode {
	ListNode(int number, const string message)
		:number_(number), message_(message)
	{}
	int number_;
	string message_;
	ListNode* next_;
};

void printList(ListNode* head)
{
	ostringstream oss;
	for (ListNode* temp = head; temp; temp = temp->next_) {
		oss << "index:" << temp->number_ << " message:" << temp->message_ << '
';
	}
	cout << oss.str() << endl;
}

// return list head
ListNode* createList(size_t count)
{
	string message;
	std::allocator<ListNode> alloc;
	ListNode *head, *current, *temp;

	for (size_t i = 0; i < count; ++i) {
		temp = alloc.allocate(sizeof(*temp));
		cin >> message;
		alloc.construct(temp, i, message);
		if (i == 0) {
			head = current = temp;
		} else {
			current->next_ = temp;
			current = temp;
		}
	}

	return head;
}

// return the new head
ListNode* reverseList(ListNode* head)
{
	ListNode *current, *next, *prev = nullptr;

	for (current = head; current; current = next) {
		next = current->next_;
		current->next_ = prev;
		prev = current;
		if (next == nullptr)
			break;
	}

	return current;
}

void listTest(size_t n)
{
	ListNode* head = createList(n);
	if (head)
		printList(head);
	ListNode* rhead = reverseList(head);
	if (rhead)
		printList(rhead);
}

} // namespace

int main(void)
{
	listTest(10);
	return 0;
}