133.md

133. Clone Graph

难度: Medium

刷题内容

原题连接

• https://leetcode.com/problems/clone-graph/description/

内容描述

Given the head of a graph, return a deep copy (clone) of the graph. Each node in the graph contains a label (int) and a list (List[UndirectedGraphNode]) of its neighbors. There is an edge between the given node and each of the nodes in its neighbors.


OJ's undirected graph serialization (so you can understand error output):
Nodes are labeled uniquely.

We use # as a separator for each node, and , as a separator for node label and each neighbor of the node.
 

As an example, consider the serialized graph {0,1,2#1,2#2,2}.

The graph has a total of three nodes, and therefore contains three parts as separated by #.

First node is labeled as 0. Connect node 0 to both nodes 1 and 2.
Second node is labeled as 1. Connect node 1 to node 2.
Third node is labeled as 2. Connect node 2 to node 2 (itself), thus forming a self-cycle.
 

Visually, the graph looks like the following:

       1
      / \
     /   \
    0 --- 2
         / \
         \_/
Note: The information about the tree serialization is only meant so that you can understand error output if you get a wrong answer. You don't need to understand the serialization to solve the problem.

解题方案

思路 1 - 时间复杂度: O(V + E)- 空间复杂度: O(V)******

DFS iterative

class Solution:
    # @param node, a undirected graph node
    # @return a undirected graph node
    def cloneGraph(self, node):
        if not node:
            return 
        
        stack = [node]
        res = UndirectedGraphNode(node.label)
        visited = {node.label: res}
        
        while stack:
            cur = stack.pop()
            if cur.label not in visited: # 这个node没有被构造，那么就构造它然后放进字典里
                new_cur = UndirectedGraphNode(cur.label) 
                lookup[cur.label] = new_cur
            for neighbor in cur.neighbors:
                if neighbor.label not in visited: # 如果是还未构造的node才放进栈里面
                    new_neighbor = UndirectedGraphNode(neighbor.label)
                    visited[neighbor.label] = new_neighbor
                    stack.append(neighbor) 
                visited[cur.label].neighbors.append(visited[neighbor.label])
        return res

思路 2 - 时间复杂度: O(V + E)- 空间复杂度: O(V)******

BFS iterative，其实就是改变一下pop的顺序而已

class Solution:
    # @param node, a undirected graph node
    # @return a undirected graph node
    def cloneGraph(self, node):
        if not node:
            return 
        
        stack = [node]
        res = UndirectedGraphNode(node.label)
        visited = {node.label: res}
        
        while stack:
            cur = stack.pop(0)
            if cur.label not in visited: # 这个node没有被构造，那么就构造它然后放进字典里
                new_cur = UndirectedGraphNode(cur.label) 
                lookup[cur.label] = new_cur
            for neighbor in cur.neighbors:
                if neighbor.label not in visited: # 如果是还未构造的node才放进栈里面
                    new_neighbor = UndirectedGraphNode(neighbor.label)
                    visited[neighbor.label] = new_neighbor
                    stack.append(neighbor) 
                visited[cur.label].neighbors.append(visited[neighbor.label])
        return res

思路 3 - 时间复杂度: O(V + E)- 空间复杂度: O(V)******

DFS recursive

class Solution:
    # @param node, a undirected graph node
    # @return a undirected graph node
    def cloneGraph(self, node):
        if not node:
            return
        
        def dfs(node):
            if node.label in visited:
                return visited[node.label]
            new_node = UndirectedGraphNode(node.label)
            visited[new_node.label] = new_node
            new_node.neighbors = [dfs(n) for n in node.neighbors]
            return new_node
        
        visited = {}
        return dfs(node)