clone-graph leetcode C++

Clone an undirected graph. Each node in the graph contains alabeland a list of itsneighbors.

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 as0. Connect node0to both nodes1and2. Second node is labeled as1. Connect node1to node2. Third node is labeled as2. Connect node2to node2(itself), thus forming a self-cycle.

Visually, the graph looks like the following:

   1
  / \
 /   \
0 --- 2
     / \
     \_/

C++

/**
 * 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<int, UndirectedGraphNode*> umap;
        return clone(node, umap);
    }
    UndirectedGraphNode *clone(UndirectedGraphNode *node, unordered_map<int, UndirectedGraphNode*> &umap) {
        if (!node) return node;
        if (umap.count(node->label)) return umap[node->label];
        UndirectedGraphNode *newNode = new UndirectedGraphNode(node->label);
        umap[node->label] = newNode;
        for (int i = 0; i < node->neighbors.size(); ++i){
            (newNode->neighbors).push_back(clone(node->neighbors[i],umap));
        }
        return newNode;
    }
};