思路：
一般这种遍历都可以通过BFS或者DFS完成，我们首先通过BFS，但是需要记住哪些节点已经拷贝过了，类似于visited，我们可以用
map<Node, Node> m 的一个map来记住哪些已经拷贝了。
具体的代码如下：
/*
// Definition for a Node.
class Node {
public:
int val;
vector<Node*> neighbors;
Node() {}
Node(int _val, vector<Node*> _neighbors) {
val = _val;
neighbors = _neighbors;
}
};
*/
class Solution {
public:
Node* cloneGraph(Node* node) {
if (!node) return nullptr;
Node* copy = new Node(node->val, {});
m[node] = copy;
stack<Node*> s;
s.push(node);
while (!s.empty()) {
Node* tmp = s.top();
s.pop();
for (auto neighbor : tmp->neighbors) {
if (m.find(neighbor) == m.end()) {
s.push(neighbor);
m[neighbor] = new Node(neighbor->val, {});
}
m[tmp]->neighbors.push_back(m[neighbor]);
}
}
return copy;
}
private:
map<Node*, Node*> m;
};
DFS:
class Solution {
public:
Node* cloneGraph(Node* node) {
if (!node) {
return NULL;
}
if (copies.find(node) == copies.end()) {
copies[node] = new Node(node -> val, {});
for (Node* neighbor : node -> neighbors) {
copies[node] -> neighbors.push_back(cloneGraph(neighbor));
}
}
return copies[node];
}
private:
unordered_map<Node*, Node*> copies;
};
