题目链接 : https://leetcode-cn.com/problems/copy-list-with-random-pointer/
题目描述:
给定一个链表，每个节点包含一个额外增加的随机指针，该指针可以指向链表中的任何节点或空节点。
要求返回这个链表的深拷贝。
示例:
示例：
输入：
{"$id":"1","next":{"$id":"2","next":null,"random":{"$ref":"2"},"val":2},"random":{"$ref":"2"},"val":1}
解释：
节点 1 的值是 1，它的下一个指针和随机指针都指向节点 2 。
节点 2 的值是 2，它的下一个指针指向 null，随机指针指向它自己。提示：
你必须返回给定头的拷贝作为对克隆列表的引用。
思路:
思路一: 可以套用与 133. 克隆图|题解链接一样方法两种遍历(DFS, BFS)
思路二: 因为是链表,所以直接先把所有节点找到, 再连线;
思路三:
这个方法十分巧妙 , 用图说明吧
代码:
思路一: DFS
"""
# Definition for a Node.
class Node:
def __init__(self, val, next, random):
self.val = val
self.next = next
self.random = random
"""
class Solution:
def copyRandomList(self, head: 'Node') -> 'Node':
lookup = {}
def dfs(head):
if not head: return None
if head in lookup: return lookup[head]
clone = Node(head.val, None, None)
lookup[head] = clone
clone.next, clone.random = dfs(head.next), dfs(head.random)
return clone
return dfs(head)BFS
"""
# Definition for a Node.
class Node:
def __init__(self, val, next, random):
self.val = val
self.next = next
self.random = random
"""
class Solution:
def copyRandomList(self, head: 'Node') -> 'Node':
from collections import deque
lookup = {}
def bfs(head):
if not head: return head
clone = Node(head.val, None, None)
queue = deque()
queue.appendleft(head)
lookup[head] = clone
while queue:
tmp = queue.pop()
if tmp.next and tmp.next not in lookup:
lookup[tmp.next] = Node(tmp.next.val, [], [])
queue.appendleft(tmp.next)
if tmp.random and tmp.random not in lookup:
lookup[tmp.random] = Node(tmp.random.val, [], [])
queue.appendleft(tmp.random)
lookup[tmp].next = lookup.get(tmp.next)
lookup[tmp].random = lookup.get(tmp.random)
return clone
return bfs(head)思路二:
"""
# Definition for a Node.
class Node:
def __init__(self, val, next, random):
self.val = val
self.next = next
self.random = random
"""
class Solution:
def copyRandomList(self, head: 'Node') -> 'Node':
if not head: return None
lookup = {}
node = head
# 创建所有节点
while node:
lookup[node] = Node(node.val, None, None)
node = node.next
node = head
# 节点连接
while node:
lookup[node].next = lookup.get(node.next)
lookup[node].random = lookup.get(node.random)
node = node.next
return lookup[head]java
class Solution {
public Node copyRandomList(Node head) {
if (head == null) return null;
Map<Node, Node> lookup = new HashMap<>();
Node node = head;
while (node != null){
lookup.put(node, new Node(node.val, null, null));
node = node.next;
}
node = head;
while (node != null){
lookup.get(node).next = lookup.get(node.next);
lookup.get(node).random = lookup.get(node.random);
node = node.next;
}
return lookup.get(head);
}
}思路三:
"""
# Definition for a Node.
class Node:
def __init__(self, val, next, random):
self.val = val
self.next = next
self.random = random
"""
class Solution:
def copyRandomList(self, head: 'Node') -> 'Node':
if not head: return None
# 复制节点
cur = head
while cur:
# 保存下一个节点
tmp = cur.next
# 后面跟着同样的节点
cur.next = Node(cur.val, None, None)
# 拼接
cur.next.next = tmp
cur = tmp
# 复制random指针
cur = head
while cur:
if cur.random:
cur.next.random = cur.random.next
cur = cur.next.next
# 拆分
cur = head
copy_head = head.next
copy_cur = copy_head
while copy_cur.next:
# 组head
cur.next = cur.next.next
cur = cur.next
# 组 copy_head
copy_cur.next = copy_cur.next.next
copy_cur = copy_cur.next
# 把链表结束置空
cur.next = copy_cur.next
copy_cur.next = None
return copy_headjava
class Solution {
public Node copyRandomList(Node head) {
if (head == null) return null;
// 复制
Node cur = head;
while (cur != null) {
Node tmp = cur.next;
cur.next = new Node(cur.val, null, null );
cur.next.next = tmp;
cur = tmp;
}
// 置随机指针
cur = head;
while (cur != null) {
if (cur.random != null) cur.next.random = cur.random.next;
cur = cur.next.next;
}
// 拆分
cur = head;
Node copy_head = cur.next;
Node copy_cur = copy_head;
while (copy_cur.next != null) {
cur.next = cur.next.next;
cur = cur.next;
copy_cur.next = copy_cur.next.next;
copy_cur = copy_cur.next;
}
// 结束标志null
cur.next = null;
return copy_head;
}
}