Clone Graph
描述
Clone an undirected graph. Each node in the graph contains a label
and a list of its neighbours
.
OJ's undirected graph serialization: Nodes are labeled uniquely.
We use #
as a separator for each node, and ,
as a separator for node label and each neighbour 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
/ \
\_/
分析
广度优先遍历或深度优先遍历都可以。
DFS
// Clone Graph
// DFS,时间复杂度O(n),空间复杂度O(n)
class Solution {
public:
UndirectedGraphNode *cloneGraph(const UndirectedGraphNode *node) {
if(node == nullptr) return nullptr;
// key is original node,value is copied node
unordered_map<const UndirectedGraphNode *,
UndirectedGraphNode *> visited;
clone(node, visited);
return visited[node];
}
private:
// DFS
static UndirectedGraphNode* clone(const UndirectedGraphNode *node,
unordered_map<const UndirectedGraphNode *,
UndirectedGraphNode *> &visited) {
// a copy already exists
if (visited.find(node) != visited.end()) return visited[node];
UndirectedGraphNode *new_node = new UndirectedGraphNode(node->label);
visited[node] = new_node;
for (auto nbr : node->neighbors)
new_node->neighbors.push_back(clone(nbr, visited));
return new_node;
}
};
BFS
// Clone Graph
// BFS,时间复杂度O(n),空间复杂度O(n)
class Solution {
public:
UndirectedGraphNode *cloneGraph(const UndirectedGraphNode *node) {
if (node == nullptr) return nullptr;
// key is original node,value is copied node
unordered_map<const UndirectedGraphNode *,
UndirectedGraphNode *> copied;
// each node in queue is already copied itself
// but neighbors are not copied yet
queue<const UndirectedGraphNode *> q;
q.push(node);
copied[node] = new UndirectedGraphNode(node->label);
while (!q.empty()) {
const UndirectedGraphNode *cur = q.front();
q.pop();
for (auto nbr : cur->neighbors) {
// a copy already exists
if (copied.find(nbr) != copied.end()) {
copied[cur]->neighbors.push_back(copied[nbr]);
} else {
UndirectedGraphNode *new_node =
new UndirectedGraphNode(nbr->label);
copied[nbr] = new_node;
copied[cur]->neighbors.push_back(new_node);
q.push(nbr);
}
}
}
return copied[node];
}
};