【Leetcode】Clone Graph

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
         / \
         \_/

/**
 * Definition for undirected graph.
 * struct UndirectedGraphNode {
 *     int label;
 *     vector<UndirectedGraphNode *> neighbors;
 *     UndirectedGraphNode(int x) : label(x) {};
 * };
 */
class Solution {
public:
    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
        unordered_map<UndirectedGraphNode *, UndirectedGraphNode *> map;
        if (node == nullptr) {
            return nullptr;
        }
        return clone(node, map);
    }
private:
    UndirectedGraphNode *clone(UndirectedGraphNode *node, 
            unordered_map<UndirectedGraphNode *, UndirectedGraphNode *> &map) {
        if (map.find(node) != map.end()) {
            return map[node];
        } 
        UndirectedGraphNode *new_node = new UndirectedGraphNode(node->label);
        map[node] = new_node;
        for (auto n : node->neighbors) {
            new_node->neighbors.push_back(clone(n, map));
        }
        return new_node;
    }
};

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