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.
#
,
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 node0
to both nodes1
and2
. - Second node is labeled as
1
. Connect node1
to node2
. - Third node is labeled as
2
. Connect node2
to node2
(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.
解法
使用一个map记录节点的值和节点指针。使用dfs深度优先搜索图,每次创建节点的时候就在map里面增加一条记录。
(注意:需要在一开始的时候就增加map记录,否则会出现死循环的问题,例如
{0,0,0}
这个图,如果等到找到节点的时候再增加记录则出错。)
错误代码
class Solution {
map<int, UndirectedGraphNode *> dict;
public:
UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
if(node == nullptr)
return node;
UndirectedGraphNode *root =new UndirectedGraphNode(node->label);
for(int i=0;i<node->neighbors.size();i++) {
if(dict.find(node->neighbors[i]->label)==dict.end())
dict[node->neighbors[i]->label] = cloneGraph(node->neighbors[i]); //在这才记录可能死循环
root->neighbors.push_back(dict[node->neighbors[i]->label]);
}
return root;
}
};
正确代码
class Solution {
map<int, UndirectedGraphNode *> dict;
public:
UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
if(node == nullptr)
return node;
UndirectedGraphNode *root =new UndirectedGraphNode(node->label);
dict[root->label] = root; // 在这里记录数据
for(int i=0;i<node->neighbors.size();i++) {
if(dict.find(node->neighbors[i]->label)==dict.end())
cloneGraph(node->neighbors[i]);
root->neighbors.push_back(dict[node->neighbors[i]->label]);
}
return root;
}
};