LintCode 137 Clone Graph Python problem solution

 describe

 Clone an undirected graph. Each node in the graph contains a label and a list of its neighbors. Nodes are labeled uniquely.

You need to return a deep copied graph, which has the same structure as the original graph, and any changes to the new graph will not have any effect on the original graph.

 

You need return the node with the same label as the input node.

 

illustrate

How we serialize an undirected graph: http://www.lintcode.com/help/graph/

Sample

Example1

Input:
{1,2,4#2,1,4#4,1,2}
Output: 
{1,2,4#2,1,4#4,1,2}
Explanation:
1------2  
 \     |  
  \    |  
   \   |  
    \  |  
      4   

 

Meanwhile, the class definition is:

"""
class UndirectedGraphNode:
     def __init__(self, x):
         self.label = x
         self.neighbors = []
"""

 

Note:  To be honest, this is the first time I encountered a similar question. When copying Python's list and dict, etc., a=[1,2,3]; b= a; b.append(4);, both a and b are [1,2,3,4]. This is shallow copy. To implement deep copying on a data structure, each part of the data structure needs to be copied separately. In this question, you need to copy the label and neighbor separately.

(Refer to Chapter 9 for the solution to this question)

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from collections import deque

"""
class UndirectedGraphNode:
     def __init__(self, x):
         self.label = x
         self.neighbors = []
"""

class Solution:
    """
    @param node: A undirected graph node
    @return: A undirected graph node
    """
    def cloneGraph(self, node):
        root = node #哪个点是入口，待会仍然从这个点开始
        if node is None:
            return node
        # write your code here
        nodes = self.getnodes(node)
        mapping = {}
        for node in nodes:
            mapping[node] = UndirectedGraphNode(node.label)
        
        for node in nodes:
            #new_node = mapping[node]
            for neighbor in node.neighbors:
                #new_neighbor = mapping[neighbor]
                #new_node.neighbors.append(new_neighbor)
                mapping[node].neighbors.append(mapping[neighbor])
                
        return mapping[root]
        
        
    def getnodes(self,node):
        queue = deque([node])
        result = set([node])
        while(queue):
            head = queue.popleft()
            for neighbor in head.neighbors:
                if(neighbor not in result):
                    result.add(neighbor)
                    queue.append(neighbor)
        return result