class Solution {
public:
    bool isBipartite(vector<vector<int>>& graph) {
        if(graph.size()==0){
            return false;
        }
        unordered_set<int>first_set;
        unordered_set<int>second_set;
        queue<int>to_process_children;
        unordered_set<int>already_used;
        int first_nenul=0;

        to_process_children.push(first_nenul);
        first_set.insert(first_nenul);
        while(!to_process_children.empty()){
            int front = to_process_children.front();
            to_process_children.pop();
            if(already_used.find(front)!=already_used.end()){
                continue;
            }
            if(graph[front].size()==0){
                continue;
            }
            if(first_set.find(front)!=first_set.end()){
                second_set.insert(graph[front].begin(), graph[front].end());
            }
            else{
                first_set.insert(graph[front].begin(), graph[front].end());
            }
            for(int i=0; i<graph[front].size();i++){
                to_process_children.push(graph[front][i]);
            }
            already_used.insert(front);
        }
        for(int i=0; i<graph.size();i++){
            if(first_set.find(i)!=first_set.end() && second_set.find(i)!= second_set.end()){
                return false;
            }
        }
        return true;

    }
};