138. Copy List with Random Pointer

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138. Copy List with Random Pointer

题目

 A linked list is given such that each node contains an additional random pointer which could point to any node in the list or null.

Return a deep copy of the list. 

解析

• 思路参考;LeetCode:Copy List with Random Pointer

1. 在原链表的每个节点后面拷贝出一个新的节点

2. 依次给新的节点的随机指针赋值，而且这个赋值非常容易 cur->next->random = cur->random->next

3. 断开链表可得到深度拷贝后的新链表

• 几个易错点：

• 插入在当前节点前或者后要分清

• copy random 指针->next理解，就是当前copy节点的random节点指向当前cur节点的random节点的下一个节点

• 分离链表是否加头结点，不加也可以吧，指针分离都要连起来

/**
 * Definition for singly-linked list with a random pointer.
 * struct RandomListNode {
 *     int label;
 *     RandomListNode *next, *random;
 *     RandomListNode(int x) : label(x), next(NULL), random(NULL) {}
 * };
 */

class Solution {
public:
	RandomListNode *copyRandomList(RandomListNode *head) {

		if (!head)
			return NULL;
		//if (!head->next) //bug: 这句话bug,不加才行！！！
		//{
		//	RandomListNode* copy = new RandomListNode(head->label);
		//	return copy;
		//}

		RandomListNode* cur = head;

		RandomListNode* temp = NULL;
		while (cur) //在每个节点后面copy节点
		{
			RandomListNode* newNode = new RandomListNode(cur->label); //bug 在之后插入

			temp = cur->next;
			cur->next = newNode;
			newNode->next = temp;
			
			cur = cur->next->next;
		}

		//每个节点copy random指针

		cur = head;
		while (cur) //bug 指针越界
		{
			if (cur->random)
			{
				cur->next->random = cur->random->next; //??->next
			}
			cur=cur->next->next;
		}

		// 将original list和copy list分开

		cur = head;
		RandomListNode* copyHead = new RandomListNode(0);
		RandomListNode* copy_cur = copyHead;

		RandomListNode* next = NULL;
		while (cur)
		{
			next = cur->next->next;

			copy_cur->next = cur->next;
			copy_cur = cur->next;

			cur->next = next;
			cur = next;

		}

		return copyHead->next;

		/*RandomListNode*p = NULL;
		p = head;
		RandomListNode* res = head->next;
		while (p->next != NULL)
		{
			RandomListNode* tmp = p->next;
			p->next = p->next->next;
			p = tmp;
		}
		return res;	*/
	}
};

题目来源

• 138. Copy List with Random Pointer