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2021-07-19

leetcode138 Copy List with Random Pointer-zh

# 138. 复制带随机指针的链表 (opens new window)

English Version (opens new window)

# 题目描述

给你一个长度为 n 的链表，每个节点包含一个额外增加的随机指针 random ，该指针可以指向链表中的任何节点或空节点。

构造这个链表的 深拷贝。 深拷贝应该正好由 n 个 全新 节点组成，其中每个新节点的值都设为其对应的原节点的值。新节点的 next 指针和 random 指针也都应指向复制链表中的新节点，并使原链表和复制链表中的这些指针能够表示相同的链表状态。复制链表中的指针都不应指向原链表中的节点 。

例如，如果原链表中有 X 和 Y 两个节点，其中 X.random --> Y 。那么在复制链表中对应的两个节点 x 和 y ，同样有 x.random --> y 。

返回复制链表的头节点。

用一个由 n 个节点组成的链表来表示输入/输出中的链表。每个节点用一个 [val, random_index] 表示：

  • val：一个表示 Node.val 的整数。
  • random_index：随机指针指向的节点索引（范围从 0 到 n-1）；如果不指向任何节点，则为  null 。

你的代码 只 接受原链表的头节点 head 作为传入参数。

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：

  • 0 <= n <= 1000
  • -10000 <= Node.val <= 10000
  • Node.random 为空（null）或指向链表中的节点。

# 解法

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
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接着设置新节点的 ramdom 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
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# 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;
    }
}
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# 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;
    }
};
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# 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;
    }
}
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# 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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# JavaScript

/**
 * // 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;
};
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# ...
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