How to print undirected graph like LeetCode's serialisation?

[pezy]

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
     / \
     \_/

Question:
Give you an undirected graph like above, print a string like 0,1,2#1,2#2,2.

Another example: 0,1,5#1,2,5#2,3#3,4,4#4,5,5#5, check this.

[pezy]

BFS in sorted way.

#include <iostream>
#include <unordered_map>
#include <unordered_set>
#include <algorithm>
#include <deque>
#include <string>
#include <sstream>

void printUndirectedGraph(UndirectedGraphNode *node) {
    std::ostringstream out;
    std::unordered_map<int, std::unordered_set<int>> map{{0, std::unordered_set<int>()}};
    std::deque<UndirectedGraphNode*> cache;
    cache.push_back(node);
    do {
        std::sort(cache.begin(), cache.end(),[](UndirectedGraphNode* n1, UndirectedGraphNode* n2){
            return n1->label < n2->label;
        });
        UndirectedGraphNode *node = cache.front(); cache.pop_front();
        out << node->label;
        auto found = map.find(node->label);
        for (UndirectedGraphNode* neighbor : node->neighbors) {
            if (map.find(neighbor->label) == map.end()) cache.push_back(neighbor);
            if (found != map.end()) {
                std::unordered_set<int> &exist = found->second;
                if (exist.find(neighbor->label) == exist.end()) out << "," << neighbor->label;
            }
            map[neighbor->label].emplace(node->label);
        }
        out << "#";
    } while (!cache.empty());
    std::string out_str = out.str();
    std::cout << out_str.substr(0, out_str.size()-1) << std::endl;
}