Leetcode 138. Copy List with Random Pointer

/**
 * 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:
    using UMP = unordered_map<RandomListNode*, RandomListNode*>;
    RandomListNode *copyRandomList(RandomListNode *head) {
        if (head == nullptr) return nullptr;

        RandomListNode* ret = new RandomListNode(head->label);
        UMP mp{{head, ret}};
        RandomListNode* pdest = solver(head, ret, mp);
        RandomListNode* psrc = head->next;

        while (psrc) {
            pdest = solver(psrc, pdest, mp);
            psrc = psrc->next;
        }
        return ret;
    }
private:
    RandomListNode* solver(RandomListNode*& psrc, RandomListNode*& pdst, UMP& mp) {
        if (psrc->random == nullptr) pdst->random == nullptr;
        else {
            UMP::iterator it = mp.find(psrc->random);
            if(it == end(mp)) {
                RandomListNode* p = new RandomListNode(psrc->random->label);
                mp[psrc->random] = p;
                pdst->random = p;
            } else {
                pdst->random = it->second;
            }
        }

        if (psrc->next == nullptr) pdst->next == nullptr;
        else {
            UMP::iterator it = mp.find(psrc->next);
            if(it == end(mp)) {
                RandomListNode* p = new RandomListNode(psrc->next->label);
                mp[psrc->next] = p;
                pdst->next = p;
            } else {
                pdst->next = it->second;
            }
        }
        return pdst ->next;
    }


};

參考後

/**
 * 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) {

        // insert a copy behind
        if (head == nullptr) return nullptr;
        RandomListNode* ret;
        RandomListNode* pSrc = head;
        RandomListNode* tmp = nullptr;

        // tmp = srcNext;
        while (pSrc) {

            RandomListNode* copy = new RandomListNode(pSrc->label);
            copy->next = pSrc->next;
            pSrc->next = copy;
            pSrc = copy->next;
        }

        pSrc = head;
        // tmp = pSrc->random
        while (pSrc) {

            if (pSrc->random != nullptr) 
                pSrc->next->random = pSrc->random->next;
            pSrc = pSrc->next->next;
        }

        ret = head->next;
        pSrc = ret->next;
        head->next = pSrc;
        // tmp = pDst;
        tmp = ret;
        while (pSrc) {
            tmp->next = pSrc->next;
            tmp = tmp->next;
            pSrc->next = tmp->next;
            pSrc= pSrc->next;
        }

        return ret;   
    }

};