面試題35. 複雜鏈表的複製

請實現 copyRandomList 函數，複製一個複雜鏈表。在複雜鏈表中，每個節點除了有一個 next 指針指向下一個節點，還有一個 random 指針指向鏈表中的任意節點或者 null。

輸入：head = [[7,null],[13,0],[11,4],[10,2],[1,0]]
輸出：[[7,null],[13,0],[11,4],[10,2],[1,0]]

算法：深度優先搜索

"""
# 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':
        def dfs(head):
            if not head: return None#head爲空返回None
            if head in visited:#head已經被遍歷，返回head對應的節點
                return visited[head]
            # 如果沒有被訪問，則創建新結點
            copy = Node(head.val, None, None)#複製值
            #節點生成以後要把visited設成true
            visited[head] = copy
            copy.next = dfs(head.next)#複製指針
            copy.random = dfs(head.random)#複製指針
            return copy
        visited = {}
        return dfs(head)

算法：廣度優先搜索

class Solution:
    def copyRandomList(self, head: 'Node') -> 'Node':
        visited = {}
    
        def bfs(head):
            if not head: return head
            clone = Node(head.val, None, None) # 創建新結點
            queue = collections.deque()
            queue.append(head)
            visited[head] = clone
            while queue:
                tmp = queue.pop()
                if tmp.next and tmp.next not in visited:
                    visited[tmp.next] = Node(tmp.next.val, [], [])
                    queue.append(tmp.next)  
                if tmp.random and tmp.random not in visited:
                    visited[tmp.random] = Node(tmp.random.val, [], [])
                    queue.append(tmp.random)
                visited[tmp].next = visited.get(tmp.next)
                visited[tmp].random = visited.get(tmp.random)
            return clone
        return bfs(head)