单链表排序——快速排序实现

利用快速排序，同向一前一后两个指针

#ifndef LIST_H_
#define LIST_H_

#include <iostream>
#include <utility>

class List {
private:
	struct ListNode {
		int _value;
		ListNode* _next;
	};

public:
	List(): _head(nullptr) {}

	~List() {
		while (nullptr != _head) {
			auto tmp = _head;
			_head = _head->_next;
			delete tmp;
		}
	}

	// 插入
	void PushBack(int value) {
		if (nullptr == _head) {
			ListNode* tmp = new ListNode();
			tmp->_value = value;
			tmp->_next = nullptr;
			_head = tmp;
		} else {
			ListNode* current = _head;

			while (nullptr != current->_next) {
				current = current->_next;
			}

			ListNode* tmp = new ListNode();
			tmp->_value = value;
			tmp->_next = nullptr;
			current->_next = tmp;
		}
	}

	// 排序
	void Sort() {
		QuickSort(_head, nullptr);
	}

	// 显示
	void Display() const {
		auto current = _head;

		while (nullptr != current) {
			std::cout << current->_value << " ";
			current = current->_next;
		}
		std::cout << std::endl;
	}

private:
	void QuickSort(ListNode* first, ListNode* last) {
		if (first != last) {
			ListNode* pivotPtr = Partition(first, last);
			QuickSort(first, pivotPtr);
			QuickSort(pivotPtr->_next, last);
		}
	}

	ListNode* Partition(ListNode* first, ListNode* last) {
		const int pivot = first->_value;
		ListNode* i = first;
		ListNode* j = first->_next;

		while (j != last) {
			if (j->_value <= pivot) {
				i = i->_next;
				std::swap(i->_value, j->_value);
			}
			j = j->_next;
		}
		std::swap(first->_value, i->_value);

		return i;
	}

	ListNode* _head;
};

#endif // LIST_H_