创新工场笔试题Copy List with Random Pointer

假设有如下一个链表：

其中，random指向该链表的任意一个节点或者NULL，请编程实现该链表的深拷贝。

解析：把新节点插入到相应的旧节点后面：

分两步

1、构建新节点random指针：new1->random = old1->random->next, new2-random = NULL, new3-random = NULL, new4->random = old4->random->next

2、恢复原始链表以及构建新链表：例如old1->next = old1->next->next, new1->next = new1->next->next

该算法时间复杂度O(N)，空间复杂度O(1)

代码：

Node *deepCopy (Node *head)
{
    Node* now = head;
    Node* next = head->next;
    while( now != NULL )
    {
         Node * copy = new Node;
         copy->value = now->value;
         copy->next  = now->next;
         now ->next  = copy;
         now         = next;
         next        = next->next;
    }
    now = head;
    while( now != NULL )
    {
         now->next->random = now->random->next;
         now = now->next->next;
    }
    Node* head2 = head->next;
    Node* newHead = head->next;
    while( head2->next != NULL )
    {
        head->next = head2->next;
        head2->next = head2->next->next;
        head = head->next;
        head2 = head2->next;
    }

    return newHead;
}

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