27.md

Restore the array from adjacent Pairs

 void dfs(unordered_map<int,vector<int>>& mp,int cur,set<int>& visited,vector<int>& ans)
    {
        if(visited.find(cur)!=visited.end()) return;
        ans.push_back(cur);
        visited.insert(cur);
        for(int x:mp[cur]){
            dfs(mp,x,visited,ans);
        }
    }
    vector<int> restoreArray(vector<vector<int>>& adjacentPairs) {
        unordered_map<int,vector<int>>mp;
        for(auto arr:adjacentPairs){
            mp[arr[0]].push_back(arr[1]);
            mp[arr[1]].push_back(arr[0]);
        }
        int head=0;
        for(auto x:mp){
            if(x.second.size()==1){
                head=x.first;
                break;
            }
        }
        set<int>visited;
        vector<int> ans;
        dfs(mp,head,visited,ans);
        return ans;
    }