133. Clone Graph

Given a reference of a node in a connected undirected graph.

Return a deep copy (clone) of the graph.

Each node in the graph contains a value (int) and a list (List[Node]) of its neighbors.

class Node:
    def init(self, val = 0, neighbors = None):
        self.val = val
        self.neighbors = neighbors if neighbors is not None else []

Test case format:

For simplicity, each node’s value is the same as the node’s index (1-indexed). For example, the first node with val == 1, the second node with val == 2, and so on. The graph is represented in the test case using an adjacency list.

An adjacency list is a collection of unordered lists used to represent a finite graph. Each list describes the set of neighbors of a node in the graph.

The given node will always be the first node with val = 1. You must return the copy of the given node as a reference to the cloned graph.

Example 1:

Input: adjList = [[2,4],[1,3],[2,4],[1,3]]
Output: [[2,4],[1,3],[2,4],[1,3]]
Explanation: There are 4 nodes in the graph.
1st node (val = 1)'s neighbors are 2nd node (val = 2) and 4th node (val = 4).
2nd node (val = 2)'s neighbors are 1st node (val = 1) and 3rd node (val = 3).
3rd node (val = 3)'s neighbors are 2nd node (val = 2) and 4th node (val = 4).
4th node (val = 4)'s neighbors are 1st node (val = 1) and 3rd node (val = 3).

Example 2:

1
2
3

Input: adjList = [[]]
Output: [[]]
Explanation: Note that the input contains one empty list. The graph consists of only one node with val = 1 and it does not have any neighbors.

Example 3:

1
2
3

Input: adjList = []
Output: []
Explanation: This an empty graph, it does not have any nodes.

Example 4:

1 2	Input: adjList = [[2],[1]] Output: [[2],[1]]

回傳dfs 走訪記錄

T:O(n), S:O(n)
class Solution:
    def cloneGraph(self, node: 'Node') -> 'Node':
        def dfs(node):
            if node in visited: return visited[node]
            
            visited[node] = Node(node.val)
            
            for nei in node.neighbors:
                visited[node].neighbors.append(dfs(nei))
                
            return visited[node]
        
        # simply return, no node 
        if not node: return None
        
        visited = {}
        clone_graph = dfs(node)
        return clone_graph

如果你覺得這篇文章很棒，請你不吝點讚 (ﾟ∀ﾟ)