剑指Offer-第2天 链表（简单）

第一题

题目链接：https://leetcode-cn.com/problems/cong-wei-dao-tou-da-yin-lian-biao-lcof/

个人题解：开一个数组，从头到尾遍历，然后反转数组即可

代码：

class Solution {
public:
    vector<int> reversePrint(ListNode* head) {
        vector<int> res;
        while(head){
            res.push_back(head->val);
            head=head->next;
        }
        reverse(res.begin(),res.end());
        return res;
    }
};

结果：

第二题

题目链接：https://leetcode-cn.com/problems/fan-zhuan-lian-biao-lcof/

个人题解：开一个 \(cur\) 和 \(head\) 一样，然后一步一步迭代即可

代码：

class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        ListNode *prev = nullptr;
        ListNode *cur = head;
        while (cur)
        {
            ListNode *next = cur->next;
            cur->next = prev;
            prev = cur, cur = next;
        }
        return prev;
    }
};

结果：

第三题

题目链接：https://leetcode-cn.com/problems/fu-za-lian-biao-de-fu-zhi-lcof/

个人题解：开一个哈希表（慢）。标答不是很能理解

个人代码 和 官方题解

class Solution {
public:
    unordered_map<Node*,Node*> hash;

    Node* copyRandomList(Node* head) {
        if(head==nullptr) return nullptr;
        if(!hash.count(head)){
            auto now=new Node(head->val);
            hash[head]=now;
            now->next=copyRandomList(head->next);
            now->random=copyRandomList(head->random);
        }
        return hash[head];
    }
};

class Solution {
public:
    Node* copyRandomList(Node* head) {
        if (head == nullptr) {
            return nullptr;
        }
        for (Node* node = head; node != nullptr; node = node->next->next) {
            Node* nodeNew = new Node(node->val);
            nodeNew->next = node->next;
            node->next = nodeNew;
        }
        for (Node* node = head; node != nullptr; node = node->next->next) {
            Node* nodeNew = node->next;
            nodeNew->random = (node->random != nullptr) ? node->random->next : nullptr;
        }
        Node* headNew = head->next;
        for (Node* node = head; node != nullptr; node = node->next) {
            Node* nodeNew = node->next;
            node->next = node->next->next;
            nodeNew->next = (nodeNew->next != nullptr) ? nodeNew->next->next : nullptr;
        }
        return headNew;
    }
};

结果（个人）

结果（官方）