LeetCode | 138. Copy List with Random Pointer

深拷贝含随机指针链表

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本文介绍了一种复杂链表结构的深拷贝方法，该链表每个节点包含一个额外的随机指针，指向链表中的任意节点或空。通过创建新链表并逐一复制节点和随机指针，实现链表的完全复制。

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.

The Linked List is represented in the input/output as a list of n nodes. Each node is represented as a pair of [val, random_index] where:

val: an integer representing Node.val
random_index: the index of the node (range from 0 to n-1) where random pointer points to, or null if it does not point to any node.

Example 1:

Input: head = [[7,null],[13,0],[11,4],[10,2],[1,0]]
Output: [[7,null],[13,0],[11,4],[10,2],[1,0]]

Example 2:

Input: head = [[1,1],[2,1]]
Output: [[1,1],[2,1]]

Example 3:

Input: head = [[3,null],[3,0],[3,null]]
Output: [[3,null],[3,0],[3,null]]

Example 4:

Input: head = []
Output: []
Explanation: Given linked list is empty (null pointer), so return null.

Constraints:

-10000 <= Node.val <= 10000
Node.random is null or pointing to a node in the linked list.
Number of Nodes will not exceed 1000.

代码：

/**
 * 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 == NULL)
            return head;
        RandomListNode* c_head = new RandomListNode(head->label);
        for(RandomListNode* p = head->next, *q = c_head; p != NULL; p = p->next)
        {
            q->next = new RandomListNode(p->label);
            q = q->next;
        }
        for(RandomListNode* p = head, *q = c_head; p != NULL; p = p->next, q = q->next)
        {
            for(RandomListNode* r = head, *s = c_head; r != NULL; r = r->next, s = s->next)
            {
                if(p->random == r)
                {
                    q->random = s;
                    break;
                }
            }
        }
        return c_head;
    }
};