[数据结构]链表操作

一、单向链表

1. 排序（插入升序）：

假设所给的链表为不带头节点的链表，由于不带头节点的链表很难操作，首先将其添加一个头节点headNode。具体操作如下

void sortLinkList(Node *&head) { // ascend
	Node *headNode = new Node();
	headNode->next = head;
	if (head != NULL) {
		Node *curr = head->next;
		head->next = NULL;
		while (curr != NULL) {
			Node *befo = headNode, *tmp = curr->next;
			while (befo->next!=NULL && befo->next->val<=curr->val) {
				befo = befo->next;
			}
			curr->next = befo->next; //befo之后即为要插入的位置
			befo->next = curr;
			curr = tmp;
		}
		head = headNode->next;
		free(headNode);
	}
}

2. 逆序：

同排序，先加上个头节点方便操作。

void reverseLinkList(Node *&head) {
	Node *nextNode = head->next;
	head->next = NULL;
	while(nextNode != NULL) {
		Node *tmp = nextNode->next;
		nextNode->next = head;
		head = nextNode;
		nextNode = tmp;
	}
}

 二、双向链表插入交换操作（带有头节点的）：

    问题描述：假设一个节点的数据结构如下，其中val为节点的值，freq为该节点的访问量。

struct DNode {
	int val;
	int freq;
	DNode *pre;
	DNode *next;
	DNode(int x=0) : val(x), freq(0), pre(NULL), next(NULL) {}
};

     每次输入一个val值对链表中该值的节点进行访问操作，链表按照访问量降序排列。

bool findDNode(DNode *&head, int elem) {
	DNode *curr = head->next;
	while(curr!=NULL && curr->val!=elem) {
		curr = curr->next;
	}
	if (curr == NULL) return false;
	curr->freq++;
	DNode *currPre = curr->pre;
	while(currPre!=head && currPre->freq<curr->freq) {
		curr->pre = currPre->pre; // new curr pre 更新当前结点的前驱
		curr->pre->next = curr; // update the new curr pre's next to curr 更新新的前驱的后继为当前结点
		currPre->next = curr->next; // update the old curr pre's next to curr's old next 更新旧的前驱节点的后继为当前结点的旧的后继
		if (currPre->next != NULL) {
			currPre->next->pre = currPre;
		}
		curr->next = currPre; // make the old curr pre to curr's new next 当前节点的后继更新为旧的前驱
		currPre->pre = curr; // update the new curr's next(the curr's old pre)'s pre to curr 新的后继的前驱为当前结点
		currPre = curr->pre; // update currPre 
	}
	return true;
}

运行结果如下：

5
1 2 3 4 5
please input the Node you want to visit:
5
(5, 1)->(1, 0)->(2, 0)->(3, 0)->(4, 0)
3
(5, 1)->(3, 1)->(1, 0)->(2, 0)->(4, 0)
1
(5, 1)->(3, 1)->(1, 1)->(2, 0)->(4, 0)
1
(1, 2)->(5, 1)->(3, 1)->(2, 0)->(4, 0)
2
(1, 2)->(5, 1)->(3, 1)->(2, 1)->(4, 0)
3
(1, 2)->(3, 2)->(5, 1)->(2, 1)->(4, 0)
3
(3, 3)->(1, 2)->(5, 1)->(2, 1)->(4, 0)
4
(3, 3)->(1, 2)->(5, 1)->(2, 1)->(4, 1)
4
(3, 3)->(1, 2)->(4, 2)->(5, 1)->(2, 1)
4
(3, 3)->(4, 3)->(1, 2)->(5, 1)->(2, 1)
4
(4, 4)->(3, 3)->(1, 2)->(5, 1)->(2, 1)

未完待补充(不复习东西都忘完了......)