[leetcode]Copy List with Random Pointer

带random随机指向链表任意地方的一个链表...

做深度拷贝.

先做next的拷贝,建立新链表.

然后把老链表的next指向新链表对应的等价节点,然后把这个新的节点的random指向老链表.

然后呢...很明显newListNode -> random -> random -> next

就是新链表random该指向的地方啦...

newListNode -> random = newListNode -> random -> random -> next;

然后再恢复oldlist的next链接...这里之前用map存好了...

好像还有一种不用map的做法

把新链表间接的插入到老链表之间...

/**
* 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 == nullptr) return head;
RandomListNode* dummy = new RandomListNode(-1);
RandomListNode* tmp = head;
RandomListNode* curr = dummy;
unordered_map<RandomListNode* , RandomListNode*> lmap;
//copy next
while(tmp != nullptr){
lmap[tmp] = tmp -> next;
RandomListNode* node = new RandomListNode(tmp -> label);
curr -> next = node;
curr = node;
tmp = tmp -> next;
}

tmp = dummy -> next;
curr = head;

//map
while(curr != nullptr){
RandomListNode* next = curr -> next;
curr -> next = tmp;
tmp -> random = curr;
curr = next;
tmp = tmp -> next;
}

curr = dummy -> next;
while(curr != nullptr){
curr -> random = curr -> random -> random == nullptr ? nullptr :  curr -> random -> random -> next;
curr = curr -> next;
}

//restore
tmp = head;
while(tmp){
tmp -> next = lmap[tmp];
tmp = tmp -> next;
}

return dummy -> next;

}
};

========update 03/08/2014======

之前因为看了某题解，还觉得很有道理。。。

但是既然你都map了为毛不做一个old到new的map就好了。。。

/**
* 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*> old2new;
RandomListNode* dummy = new RandomListNode(-1);
RandomListNode* tmp = head;
RandomListNode* curr = dummy;
while (tmp) {
RandomListNode* newNode = new RandomListNode(tmp->label);
old2new[tmp] = newNode;
curr->next = newNode;
curr = curr -> next;
tmp = tmp->next;
}
tmp = head;
while (tmp) {
if (tmp->random) {
old2new[tmp]->random = old2new[tmp->random];
}
tmp = tmp-> next;
}
return dummy->next;
}
};