面试题 35. 复杂链表的复制

题目描述

请实现 copyRandomList 函数，复制一个复杂链表。在复杂链表中，每个节点除了有一个 next 指针指向下一个节点，还有一个 random 指针指向链表中的任意节点或者 null。

 

示例 1：

输入：head = [[7,null],[13,0],[11,4],[10,2],[1,0]]
输出：[[7,null],[13,0],[11,4],[10,2],[1,0]]

示例 2：

输入：head = [[1,1],[2,1]]
输出：[[1,1],[2,1]]

示例 3：

输入：head = [[3,null],[3,0],[3,null]]
输出：[[3,null],[3,0],[3,null]]

示例 4：

输入：head = []
输出：[]
解释：给定的链表为空（空指针），因此返回 null。

 

提示：

• -10000 <= Node.val <= 10000
• Node.random 为空（null）或指向链表中的节点。
• 节点数目不超过 1000 。

 

注意：本题与主站 138 题相同：https://leetcode.cn/problems/copy-list-with-random-pointer/

 

解法

• 相比正常的克隆链表，多了一步操作，克隆随机指针。
• 随机指针并不是读取时进行随机指向，而是没有规律。但可以确定的是，随机指向的对象都是现存的节点或 null。
• 而难点在于克隆随机指针，如克隆链表头节点时，随机指针指向链尾，而链尾还未创造出来。
• 对此，需要先完成链表的基础克隆，再回头关注随机指针。

哈希表

• 使用哈希表记录所有节点， key 为原节点，value 为克隆节点。
• 遍历链表，完成记录，克隆节点暂时只记录对应的 val。
• 再次遍历，完善克隆节点的 next 与 random。

原地算法

首先，遍历链表，完成对每个旧节点的复制。

A -> B -> C -> D -> null

=>

A -> A1 -> B -> B1 -> C -> C1 -> D -> D1 -> null

接着设置新节点的 random 指针。

然后遍历链表，修改旧节点和新节点的指向，将旧节点指向下一个旧节点，而新节点指向下一个新节点。

最后返回第一个新节点即可。

Python3

"""
# Definition for a Node.
class Node:
    def __init__(self, x: int, next: 'Node' = None, random: 'Node' = None):
        self.val = int(x)
        self.next = next
        self.random = random
"""


class Solution:
    def copyRandomList(self, head: 'Node') -> 'Node':
        if head is None:
            return None

        cur = head
        while cur:
            node = Node(cur.val, cur.next)
            cur.next = node
            cur = node.next

        cur = head
        while cur:
            cur.next.random = None if cur.random is None else cur.random.next
            cur = cur.next.next

        copy = head.next
        cur = head
        while cur:
            next = cur.next
            cur.next = next.next
            next.next = None if next.next is None else next.next.next
            cur = cur.next
        return copy

Java

/*
// Definition for a Node.
class Node {
    int val;
    Node next;
    Node random;

    public Node(int val) {
        this.val = val;
        this.next = null;
        this.random = null;
    }
}
*/

class Solution {
    public Node copyRandomList(Node head) {
        if (head == null) {
            return null;
        }

        Node cur = head;
        while (cur != null) {
            Node node = new Node(cur.val);
            node.next = cur.next;
            cur.next = node;
            cur = node.next;
        }

        cur = head;
        while (cur != null) {
            cur.next.random = cur.random == null ? null : cur.random.next;
            cur = cur.next.next;
        }

        Node copy = head.next;
        cur = head;
        while (cur != null) {
            Node next = cur.next;
            cur.next = next.next;
            next.next = next.next == null ? null : next.next.next;
            cur = cur.next;
        }
        return copy;
    }
}

C++

/*
// 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) {
        if (!head) {
            return nullptr;
        }
        Node* cur = head;
        while (cur) {
            Node* node = new Node(cur->val);
            node->next = cur->next;
            cur->next = node;
            cur = node->next;
        }

        cur = head;
        while (cur) {
            cur->next->random = cur->random ? cur->random->next : nullptr;
            cur = cur->next->next;
        }

        Node* copy = head->next;
        cur = head;
        while (cur) {
            Node* next = cur->next;
            cur->next = next->next;
            next->next = next->next ? next->next->next : nullptr;
            cur = cur->next;
        }
        return copy;
    }
};

C#

/*
// Definition for a Node.
public class Node {
    public int val;
    public Node next;
    public Node random;

    public Node(int _val) {
        val = _val;
        next = null;
        random = null;
    }
}
*/

public class Solution {
    public Node CopyRandomList(Node head) {
        if (head == null) {
            return null;
        }

        Node cur = head;
        while (cur != null) {
            Node node = new Node(cur.val);
            node.next = cur.next;
            cur.next = node;
            cur = node.next;
        }

        cur = head;
        while (cur != null) {
            cur.next.random = cur.random == null ? null : cur.random.next;
            cur = cur.next.next;
        }

        Node copy = head.next;
        cur = head;
        while (cur != null) {
            Node next = cur.next;
            cur.next = next.next;
            next.next = next.next == null ? null : next.next.next;
            cur = cur.next;
        }
        return copy;
    }
}

JavaScript

• 哈希表

/**
 * // Definition for a Node.
 * function Node(val, next, random) {
 *    this.val = val;
 *    this.next = next;
 *    this.random = random;
 * };
 */

/**
 * @param {Node} head
 * @return {Node}
 */
var copyRandomList = function (head) {
    if (head == null) {
        return head;
    }

    let cur = head;
    const map = new Map();
    while (cur != null) {
        map.set(cur, new Node(cur.val));
        cur = cur.next;
    }

    const res = new Node();
    let newCur = res;
    cur = head;
    while (cur != null) {
        const node = map.get(cur);
        node.random = map.get(cur.random);
        newCur.next = node;
        newCur = node;
        cur = cur.next;
    }

    return res.next;
};

• 原地算法

/**
 * // Definition for a Node.
 * function Node(val, next, random) {
 *    this.val = val;
 *    this.next = next;
 *    this.random = random;
 * };
 */

/**
 * @param {Node} head
 * @return {Node}
 */
var copyRandomList = function (head) {
    if (head == null) {
        return null;
    }
    let cur = head;
    while (cur != null) {
        let node = new Node(cur.val, cur.next);
        cur.next = node;
        cur = node.next;
    }

    cur = head;
    while (cur != null) {
        cur.next.random = cur.random == null ? null : cur.random.next;
        cur = cur.next.next;
    }

    let copy = head.next;
    cur = head;
    while (cur != null) {
        let next = cur.next;
        cur.next = next.next;
        next.next = next.next == null ? null : next.next.next;
        cur = cur.next;
    }
    return copy;
};

Go

/**
 * Definition for a Node.
 * type Node struct {
 *     Val int
 *     Next *Node
 *     Random *Node
 * }
 */

func copyRandomList(head *Node) *Node {
    if head == nil {
        return nil
    }

    cur := head
    for cur != nil {
        node := &Node{
            Val: cur.Val,
            Next: cur.Next,
            Random: nil,
        }
        cur.Next = node
        cur = node.Next
    }

    cur = head
    for cur != nil {
        if cur.Random == nil {
            cur.Next.Random = nil
        } else {
            cur.Next.Random = cur.Random.Next
        }
        cur = cur.Next.Next
    }

    copy := head.Next
    cur = head
    for cur != nil {
        next := cur.Next
        cur.Next = next.Next
        if (next.Next == nil) {
            next.Next = nil
        } else {
            next.Next = next.Next.Next
        }
        cur = cur.Next
    }
    return copy
}

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