[LeetCode] 133. Clone Graph 克隆无向图
Clone an undirected graph. Each node in the graph contains a label and a list of its neighbors.
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 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 node0to both nodes1and2. - Second node is labeled as
1. Connect node1to node2. - Third node is labeled as
2. Connect node2to node2(itself), thus forming a self-cycle.
Visually, the graph looks like the following:
1
/ \
/ \
0 --- 2
/ \
\_/
对图的遍历就是两个经典的方法DFS和BFS，和138. Copy List with Random Pointer思路一样，用一个HashMap记录原图节点和复制图节点间的对应关系，以防止重复建立节点，key存原始值，value存copy的值，用DFS,BFS方法遍历帮助拷贝neighbors的值。和那题的不同在于遍历原图相对比linked list的情况复杂一点。可以用BFS或DFS来遍历原图。而HashMap本身除了记录对应关系外，还有记录原图中每个节点是否已经被visit的功能。
Java: DFS
public class Solution {
private HashMap<Integer, UndirectedGraphNode> map = new HashMap<>();
public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
return clone(node);
}
private UndirectedGraphNode clone(UndirectedGraphNode node) {
if (node == null) return null;
if (map.containsKey(node.label)) {
return map.get(node.label);
}
UndirectedGraphNode clone = new UndirectedGraphNode(node.label);
map.put(clone.label, clone);
for (UndirectedGraphNode neighbor : node.neighbors) {
clone.neighbors.add(clone(neighbor));
}
return clone;
}
}
Java: BFS
/**
* Definition for undirected graph.
* class UndirectedGraphNode {
* int label;
* ArrayList<UndirectedGraphNode> neighbors;
* UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); }
* };
*/
public class Solution {
/**
* @param node: A undirected graph node
* @return: A undirected graph node
*/
public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
if(node == null)
return null;
HashMap<UndirectedGraphNode, UndirectedGraphNode> hm = new HashMap<UndirectedGraphNode, UndirectedGraphNode>();
LinkedList<UndirectedGraphNode> stack = new LinkedList<UndirectedGraphNode>();
UndirectedGraphNode head = new UndirectedGraphNode(node.label);
hm.put(node, head);
stack.push(node);
while(!stack.isEmpty()){
UndirectedGraphNode curnode = stack.pop();
for(UndirectedGraphNode aneighbor: curnode.neighbors){//check each neighbor
if(!hm.containsKey(aneighbor)){//if not visited,then push to stack
stack.push(aneighbor);
UndirectedGraphNode newneighbor = new UndirectedGraphNode(aneighbor.label);
hm.put(aneighbor, newneighbor);
}
hm.get(curnode).neighbors.add(hm.get(aneighbor));
}
}
return head;
}
}
Java: BFS
/**
* Definition for undirected graph.
* class UndirectedGraphNode {
* int label;
* ArrayList<UndirectedGraphNode> neighbors;
* UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); }
* };
*/
public class Solution {
/**
* @param node: A undirected graph node
* @return: A undirected graph node
*/
public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
if (node == null) {
return null;
}
HashMap<UndirectedGraphNode, UndirectedGraphNode> hm = new HashMap<UndirectedGraphNode, UndirectedGraphNode>();
LinkedList<UndirectedGraphNode> queue = new LinkedList<UndirectedGraphNode>();
UndirectedGraphNode head = new UndirectedGraphNode(node.label);
hm.put(node, head);
queue.add(node);
while (!queue.isEmpty()) {
UndirectedGraphNode currentNode = queue.remove();
for (UndirectedGraphNode neighbor : currentNode.neighbors) {
if (!hm.containsKey(neighbor)) {
queue.add(neighbor);
UndirectedGraphNode newNeighbor = new UndirectedGraphNode(neighbor.label);
hm.put(neighbor, newNeighbor);
}
hm.get(currentNode).neighbors.add(hm.get(neighbor));
}
}
return head;
}
}
Python: DFS
class UndirectedGraphNode:
def __init__(self, x):
self.label = x
self.neighbors = []
class Solution:
def cloneGraph(self, node):
def dfs(input, map):
if input in map:
return map[input]
output = UndirectedGraphNode(input.label)
map[input] = output
for neighbor in input.neighbors:
output.neighbors.append(dfs(neighbor, map))
return output
if node == None: return None
return dfs(node, {})
Python: BFS
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):
if node is None:
return None
cloned_node = UndirectedGraphNode(node.label)
cloned, queue = {node:cloned_node}, [node]
while queue:
current = queue.pop()
for neighbor in current.neighbors:
if neighbor not in cloned:
queue.append(neighbor)
cloned_neighbor = UndirectedGraphNode(neighbor.label)
cloned[neighbor] = cloned_neighbor
cloned[current].neighbors.append(cloned[neighbor])
return cloned[node]
C++：DFS
class Solution {
public:
UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
if(!node) return NULL;
unordered_map<UndirectedGraphNode*, UndirectedGraphNode*> ht;
stack<UndirectedGraphNode*> s;
s.push(node);
ht[node] = new UndirectedGraphNode(node->label);
while(!s.empty()) {
UndirectedGraphNode *p1 = s.top(), *p2 = ht[p1];
s.pop();
for(int i=0; i<p1->neighbors.size(); i++) {
UndirectedGraphNode *nb = p1->neighbors[i];
if(ht.count(nb)) {
p2->neighbors.push_back(ht[nb]);
}
else {
UndirectedGraphNode *temp = new UndirectedGraphNode(nb->label);
p2->neighbors.push_back(temp);
ht[nb] = temp;
s.push(nb);
}
}
}
return ht[node];
}
};
C++: BFS
class Solution {
public:
UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
if(!node) return NULL;
UndirectedGraphNode *p1 = node;
UndirectedGraphNode *p2 = new UndirectedGraphNode(node->label);
unordered_map<UndirectedGraphNode*, UndirectedGraphNode*> ht;
queue<UndirectedGraphNode*> q;
q.push(node);
ht[node] = p2;
while(!q.empty()) {
p1 = q.front();
p2 = ht[p1];
q.pop();
for(int i=0; i<p1->neighbors.size(); i++) {
UndirectedGraphNode *nb = p1->neighbors[i];
if(ht.count(nb)) {
p2->neighbors.push_back(ht[nb]);
}
else {
UndirectedGraphNode *temp = new UndirectedGraphNode(nb->label);
p2->neighbors.push_back(temp);
ht[nb] = temp;
q.push(nb);
}
}
}
return ht[node];
}
};
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