[Linked List]Copy List with Random Pointer

Total Accepted: 53943 Total Submissions: 209664 Difficulty: Hard

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.

(M) Clone Graph

o(n)空间复杂度,代码比价简单。网上还流传一种o(1)空间复杂度的解法，大致的过程就是先拷贝next结点，再连接随机结点，最后分离链表。

/**
 * 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) {
        unordered_map<RandomListNode*,RandomListNode*> umap;
        RandomListNode* newHead  = NULL;
        RandomListNode* cur      = head;
        RandomListNode* node_pre = NULL;
        RandomListNode* node     = NULL;
        while(cur){
            node      = new RandomListNode(cur->label);
            umap[cur] = node;
            cur == head ? newHead = node :node_pre->next = node;
            node_pre  = node;
            cur       = cur->next;
        }
        cur = head;
        while(cur){
            umap[cur]->random = cur->random ? umap[cur->random] : NULL;
            cur               = cur->next;
        }
        return newHead;
    }
};

Next challenges: (M) Clone Graph