剑指 Offer 35. 复杂链表的复制

思路

方法一：哈希表

/*
// Definition for a Node.
class Node {
public:
    int val;
    Node* next;
    Node* random;
    
    Node(int _val) {
        val = _val;
        next = NULL;
        random = NULL;
    }
};
*/
class Solution {
public:
    Node* copyRandomList(Node* head) {
        unordered_map<Node *, Node *> mp;
        Node *p = head;
        while(p != NULL) {
            mp[p] = new Node(p->val);
            p = p->next;
        }

        p = head;
        while(p != NULL) {
            mp[p]->next = mp[p->next];
            mp[p]->random = mp[p->random];
            p = p->next;
        }

        return mp[head];

    }
};

复杂度分析

时间复杂度：O(n)。

空间复杂度：O(n)。长度为n的链表，需要构造一个大小为n的<Node*, Node*>的哈希表，所以空间复杂度为O(n)。

方法二：迭代新旧节点交错的链表

/*
// Definition for a Node.
class Node {
public:
    int val;
    Node* next;
    Node* random;
    
    Node(int _val) {
        val = _val;
        next = NULL;
        random = NULL;
    }
};
*/
class Solution {
public:
    /*
        Old List: A --> B --> C --> D
        InterWeaved List: A --> A' --> B --> B' --> C --> C' --> D --> D'
    */
    Node* copyRandomList(Node* head) {
        if(head == NULL)
            return NULL;
        //将1->2->3 拼为 1 -> 1`-> 2 -> 2`-> 3 -> 3`
        Node *p = head;
        while(p != NULL) {
            Node *newNode = new Node(p->val);
            newNode->next = p->next;
            p->next = newNode;
            p = newNode->next;
        }

        //连接random指针
        p = head;
        while(p != NULL) {
            if(p->random)
                p->next->random = p->random->next;
            else
                p->next->random = NULL;
            p = p->next->next;
        }

        //分离两个链表
        p = head;
        Node *newHead = head->next;
        Node *q;
        while(p != NULL) {
            q = p->next;
            p->next = q->next;
            p = q->next;
            if(p)
                q->next = p->next;
            else   
                q->next = NULL;
        }

        return newHead;
    }
};

复杂度分析

时间复杂度：O(n)

空间复杂度：O(1)