[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 #.

1. First node is labeled as 0. Connect node 0 to both nodes 1 and 2.
2. Second node is labeled as 1. Connect node 1 to node 2.
3. 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
         / 
         \_/
 

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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