随机链表的复制

随机链表的复制(深拷贝)

1、题目

图1

2、题解

哈希表

建立一个哈希表，key值为原链表结点，value为新链表结点，根据原链表构建新链表的引用指向，最后返回新链表的头节点。

"""
# 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: 'Optional[Node]') -> 'Optional[Node]':
        if not head: return None
        dic = {}
        cur = head
        while cur:
            dic[cur] = Node(cur.val)
            cur = cur.next
        cur = head
        while cur:
            dic[cur].next = dic.get(cur.next)
            dic[cur].random = dic.get(cur.random)
            cur= cur.next
        
        return dic[head]

拼接+拆分

考虑构建\(原节点1\rightarrow新节点1\rightarrow原节点2\rightarrow新节点2…\)的拼接链表，这样在访问原节点的random指向节点的同时可以找到对应新节点的random指向节点。

"""
# 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 not head: return
        cur = head
        # 1. 复制各节点，并构建拼接链表
        while cur:
            tmp = Node(cur.val)
            tmp.next = cur.next
            cur.next = tmp
            cur = tmp.next
        # 2. 构建各新节点的 random 指向
        cur = head
        while cur:
            if cur.random:
                cur.next.random = cur.random.next
            cur = cur.next.next
        # 3. 拆分两链表
        cur = res = head.next
        pre = head
        while cur.next:
            pre.next = pre.next.next
            cur.next = cur.next.next
            pre = pre.next
            cur = cur.next
        pre.next = None # 单独处理原链表尾节点
        return res      # 返回新链表头节点